Probably more frequently than you realise. More recently in the UK news there have been a couple of high-profile cases:
http://news.bbc.co.uk/1/hi/uk/3115405.stm
http://news.bbc.co.uk/1/hi/uk/2988208.stm
and if it really is true that:
a "report from the U.S. Dept. of Justice... {indicates] that retrospective DNA testing in the USA has shown that 1/3 of men who have been through the entire justice system of arrest, trial and incarceration are innocent."
http://www.ukmm.org.uk/camp/rapealleg.htm
Then the number of innocent men whose lives and careers have been damaged as a result of false allegations and mis-handled investigations is staggering!
[ 08-05-2003, 09:12 AM: Message edited by: Skunk ]