Okay, before this goes any further, I just want you guys to know that I'm not trying to be arrogant or pushy. This is just a friendly conversation, right?
And stepping back from this conversation, I think this is just an intellectual disagreement, and by that I mean, none of us are really right, we just have different approaches to the game. I can totally see how this is a cool card for some of you.
So rather than argue that Eater is bad, I'd rather just explain to you guys why I personally don't like it.
I'm a Johhny/Spike, according to the test on Wizards' site. I'm not a Johnny in that I'm not too big on combo-decks, (Not to say they don't have their place in my heart), and I'm not a Spike in that I'm not ultra competetive, and I don't only care about winning. I'm a Spike in that what interests me most about magic is the mental challenge - high-level strategy is very important to me, as is knowing how to build the best deck I can. But I'm a Johnny in that I want to win in the most creative way possible. These two forces pull at each other in different ways. I frequent local tourneys, but I always go with a rogue deck. I play lots of casual magic, but my casual deck often sacrifices flavor for efficiency.
So my first criteria for liking a card is whether or not it is a competitive card. Eater of Days is not tourney viable, if only because its potentially a huge liability. I understand that that doesn't matter to most of you, and to an extent it doesn't matter to me. It only matters to me in that I appreciate all cards that are tourney viable, but I don't necessarily shun the ones that aren't. So the Spike in me sees little value in Eater, but that doesn't mean the Johnny can't.
But flavor-wise, Eater is a Timmy card, not a Johnny card. That doesn't mean I don't think the card is cool, but my goofball casual decks tend to aim for something more creative than, "I smash you with big thingy."
Still, that doesn't mean that I have absolutely no urge to try to find a use for the card, but that urge tends to come from my Spike side, not my Johnny side. I look at Eater and think, "How can I abuse this," not, "Wouldn't this be a fun way to kill somebody." In my opinion, its not a fun way to kill somebody, at least not any more. We've all seen death-by-giant-beatstick before.
Yes you can combo Eater with Bonesplitter, Fireshrieker, and Lightning Greaves, but that's 4 cards and 13 mana. For 4 cards and less mana I can give you a much more interesting combo. Note that I said "interesting" not "better." For 4 cards and 13 mana I could probably give you a much more efficient combo too, but that's not the point. The point is that clunky inefficent combos should, in my opinion, do something more creative than just power up a big monster.
But that doesn't mean I'm not willing to try and build a deck involving Eater of Days, its just that Eater has to appeal to my Spike side. The allure of Eater of Days, for me, lies not in simply winning with the card, but in using him in a competetive deck.
So, from a Spike's point of view, what makes this card alluring? Is it the 9/8 flying trample? Not exactly.
Randy Beuler said something about two kinds of cards that get restricted. The first kind are those whose effects are simply too good, no matter how much they cost. I think they put Dream Halls and Mind Over Matter in this category. Is a 9/8 flying trample broken in itself? No, it seems like the type of creature that should be allowed to exist. The other type of card that gets restricted is the undercosted type. Ancestral Recall, for example. There's nothing broken about drawing three cards, there's just something broken about doing it for only one mana.
What makes Eater of Days abusable is it's low casting cost.
So, from a Spike's point of view, there are two important facets to this card:
1) Eater of Days is a liability, therefore it does not make a good primary kill condition. Eater of Days is better as a back-up plan, (That's why I made the comparison to Platinum Angel ealier).
2) Eater of Days' strength lies in its low casting cost.
Therefore, I would want to build a deck that respected both of these premises, and I think that is hard to do and still build a decent deck. Support cards for the Eater need to be useful without the Eater.
Taken individually, most of the support cards you guys have mentioned can be very useful with and Eater of Days, however throwing them all in the samedeck seems silly.
The most efficient and most universally useful support cards are Lightning Greaves and Stifle, and looking at it again, I will admit that you can probably build a decent deck with those, but it still just doesn't quite cut the mustard for me.
Consider Stifle + Eater. This is essentially a better costed Big Furry Monster.
But is the Stifle really useful without Eater. As a disruption card, yes, Stifle is certainly useful, but if you need to keep one in hand for a combo, you are esentially turning it into dead card. It's only your 2nd, 3rd, and 4th Stifle that aren't dead cards. Plus, because Stifle counts as disruption, you run the risk of not having anything to disrupt.
Plus, all Stifle really does is remove the liability from Eater, it doesn't make it a better card. Eater will still be suseptible to creature control. Sure, when it dies you won't have to live through handing your opponent a Time Stretch, but you've lost more card advantage, losing the use of both your Eater and your Stifle.
Plus, you open yourself up to being disrupted by a counterspell. Sure, the Eater can be countered too, but when it is, you don't lose two turns. With Stifle, the player who has counters but little creature control can ruin your day by countering the Stifle - an option they didn't have before.
Also, by comboing with Stifle you are essentialy rasing the total mana cost by one blue, which, clock-wise, only buys you back one of your lost turns, not both of them. Paying four mana and two turns means you attack on round 7. Paying five mana and no turns means you attack on round 6. It's better, yes, but is it really worth the card disadvantage and increased suseptibility to disruption?
Lightning Greaves is much more reliable than Stifle, but it doesn't do much about givng your opponent two free turns, (athough haste pretty much buys you back an extra turn). Instant speed removal can still slip in before the Greaves attach, meaning that in many scenarios, you're just as screwed with the Greaves as you are without them.
And finally, the best way to integrate all of your ideas into a competetive deck would be to play an affintiy-esque type deck, in which case Lodestone Myr is a much better play at 4 mana.
Anyway, I'm way too long-winded. My point isn't that Eater isn't fun and potentially useful, just that it doesn't fit my taste and style of play. I hope what I wrote here will help you have fun with a card that I just can't bring myself to use.