I see Nuutti just posted this to the primes list:
http://groups.yahoo.com/group/primen.../message/11554
A new largest known Proth and non-Mersenne prime, 3*2145353+1, at 645817 digits, a factor of the Fermat number 2^(2^2145351)+1, discovered by John Cosgrave's group. This Fermat number is now the largest known composite Fermat number, and has too many digits to even comprehend!
Looks like a good month for large prime discoveries. I predict: SoB will be next!