I think a fair number of those in favor of some sort of fee are donating. My setup is smaller, and I'm not bothered by donating or the prospect of a fee. They are providing a service (that bit of obviousness isn't directed at you - we're mostly on the same page, I'd assume, in most regards in this matter), and at a point where it was easier to manage, no fee was just fine.

In general and at the community:

It kind of reminds me of someone who's a good baker making cupcakes as a hobby-job, earning a bit here and there from people as the news about the deliciousness of said cupcakes spreads word-of-mouth. At some point, the person realizes they can either scale back in order to keep the wagon from flying off the wheels from their day job, or whatever you wish to imagine, since by trying to keep all plates spinning might cause the quality of the cupcakes to diminish. In this case, since the site tends to be the point of complaint, the hobby baker lacks time to decorate the cupcakes as nicely as before, so some customers stop buying, OR, the hobby baker can take it to the next level, charge a bit more for the cupcakes, and, yes, still lose are few customers, but by improving on their craft, draws in more customers that are willing to pay a little more, while still saving a bit than if they had gone to some flashier large-scale baker, who charges more but the actual cupcakes really aren't any better.

Perhaps a low flat fee, with also an option to donate, may be worth considering. In stead of 1% or even 0.5%, you charge only 0.25% (or whatever), which would still undercut competition and be low enough to attract people, and it's low enough that many users already donating won't have the attitude of "Well, now I'm paying, so why should I bother donating?" I don't know what it costs to run the operation. Not at all, so the numbers are a little arbitrary. I know most pools I've used charge 1% or more. I used Slush's pool for a while an thought it was fine, even with the fee, and at the time I left, the stat pages were no better, the look of the site was no better, and so on and so forth. Hell, even pools charging a considerably high fee ask for donations. This may rub some people the wrong way, but I'll just go ahead an say it: for a community of people that go on ad nauseam about their Libertarian, capitalist ideals, I see a whole lot of hands sticking out asking for donations for fuck all. (Don't get it twisted, one sees this everywhere sans gushing adoration for Libertarian ideals, which are always fine by me as long as those doing the gushing abide by them - the whole' practice what you preach' thing.) Eligius is a service, and generally a damn fine one at that. I love the fact that it is offered for free and people can decide what it's worth to them, but in the long run the altruism will most likely not be reciprocated may the majority, and things start to break down.

 I grow irritated when people come here bitching about not getting payouts fast and all kinds of other crap when they are using a service that is gratis. If the operators were thieves, or payouts were tied up for weeks, that would be cause for action. You use a free pool and it takes longer to get some issue ironed out, what the fuck else do you expect? Seriously?

To wrap up this monster of a post, put pen to paper, figure out how much you need to get where you want to go, and a little beyond, and derive a modest fee. Yeah, you'll take a hit in the amount of donations you're receiving, but you probably notice a fluctuation anyways as difficulty rises and some miners feel they can no longer afford to donate. Still, others will continue to reward you for quality work. The only thing to add is that by adding a fee, you will be open to a little scrutiny when the stats go into fail-safe mode every other day, and so on. As soon as you attach even the smallest fee to your service, the majority begins to feel even more entitled... And to an extent they will be, but only like 0.5% more than they were when it was all free and whatnot.