I don't know if this is exactly a feature, or a combination of features, but try a search for [Allen Brinkley]:

http://www.google.com/search?hl=en&lr=&rls=GGGL%2CGGGL%3A2006-10%2CGGGL%3Aen&q=allen+brinkley&btnG=Search

The first result is from the Columbia University website, for Alan (rather than Allen) Brinkley, the university's provost, and the man I was actually looking for.

There's no "Did you mean?", but somehow Google has correctly interpreted the query, even though "Allen" doesn't appear on the Columbia page.

I guess there are three possibilities, or perhaps a combination of them come into play:

1) A number of sites linking to the Columbia page use the word "Allen"
2) Accumulated data from Google searches suggests that people who search for "Allen" may in fact be searching for "Alan". But in that case, why is there no "Did you mean?" Why is Google sure enough of what I'm looking for to give me the right answer?
3) The search engine has been programmed with variations of spellings of common names, and brings up the likeliest page, whatever spelling you used

Note that further down the SERPs the name "Allan" appears in bold: again, not what I typed, but Google interprets my search as though I did.

All odd, but however it's managed, it brings up the right result. But how does it work?

Though maybe it has something to do with the fact that Google sees "Allen" and "Allan" as interchangeable, and "Allan" DOES appear on the Columbia page.

Sorry to go on about this, but it is both surprising and nice. No such luck with Yahoo! or MSN:

http://search.yahoo.com/search?ei=UTF-8&fr=sfp&p=allen+brinkley
http://search.msn.com/results.aspx?q=allen+brinkley&FORM=QBHP

Alan Brinkley, provost of Columbia, doesn't appear on the first page of the SERPs on either search engine, though Yahoo! gets to him through the "Did you mean" feature.