Finally!!! A significant find during a Challenge. :) On 24 Apr 2010 11:40:07 UTC, PrimeGrid's 321 Prime Search found another Mega Prime:
The prime is 1,833,429 digits long and enters Chris Caldwell's The Largest Known Primes Database ranked 17th overall. This is the second mega prime for the 3*2^n-1 form, and it is the third largest found mega-digit prime using LLR. The discovery was made by David Mumper (Mumps) of the United States using an AMD Quad-Core Opteron 2378 with 8 GB RAM running Linux. This computer took just over 15 hours 24 minutes to complete the primality test. David is a member of the SETI.USA team. Official announcement and decimal representation of the prime.