QUOTE(thekohser @ Tue 18th January 2011, 7:23am)
Did we discuss anywhere here the $2 million gift to the WMF made by an anonymous donor, ... Will that donor ever be identified (such as on a Form 990 to the IRS)?
No, non-profit foundations are not required to disclose their donors.
QUOTE(thekohser @ Tue 18th January 2011, 7:23am)
... how common are anonymous donations -- of that magnitude -- to any organization?
In any funding campaign one typically secures as much as 50% of the anticipated total before the campaign is publicly announced, through this sort of "keystone" donors. In most organizations, this donation would have been announced toward the end, but not at the end. If course, in the same way there are "soft starts" (or "silent periods") at the beginning, some organizations have a "soft close" and continue the campaign for some time after it concludes, especially if it generated momentum.
QUOTE(thekohser @ Tue 18th January 2011, 7:23am)
What sort of controversy or attention is the donor seeking to avoid?
That is a very interesting question. Anonymous donations like this are often from insiders, from those who might be perceived as having a conflict of interest, or from people who do not wish to be associated with the cause. They are usually from individuals (as opposed to foundations, who do have to report their giving on 990s). A campaign will usually want to publicize a big donation like this one, so the anonymity and timing -- like the rest of Wikipedia -- are a little weird.