First of all, 14 million isn't all that much. Consider the traffic Wikipedia serves, the vast amount of content it is storing, that's not going to be cheap.

Second, I'd rather have Jimmy Wales' face staring at me once a year, than random ads that are far trickier to filter out.

Therefore, I donated, and will do so again, if I can afford it. Wikipedia is a great service, the least I can do is to help them with a little donation. And while the begging banner got old very fast, it's still miles better than the alternatives.