The playlist population is so low now that I feel like if anyone wants to grab these achievements with me it should be no problem.
10k GamerScore! - 11/30/2008
20k GamerScore! - 7/24/2009
30k Gamerscore! - 5/26/2010
40k Gamerscore! - 12/11/2011
Xbox #1: March 25th 2008 - February 15th 2009
Xbox #2: February 25th 2009 - ?