JonW - 1:40 pm on Dec 15, 2010 (gmt 0)
Kinda a pet of mine.
Robert very correctly points out that news interest can skew trends for certain terms, however, its often easy to find other highly correlated terms that aren't effected.
A favorite in recent months. "foreclosure". A horrible term for trending because every time BofA does something that makes news the trend gets messed up.
But everyone who has the unfortunate experience gets a letter called a "notice of default". Some, immediately go to Google and look up what that is.
To estimate the number of foreclosures using Google query logs, use the later term.
As for flu trends, "stuffy nose" may be better than "flu"