No problems with achievements not unlocking but every now and then my Xbox decides to delete all my Deniable Ops progress. No idea why. Don't mind so much as I've already got the full 1250G and I'm always playing Hunter. Kinda sucks that all my Infiltration and Last Stand progress is gone though, liked having them all done and don't plan to do them again (don't like those modes really) only to have it all wiped again.
MW2 - A's Creed - Pure - SC Conviction - CoD 4 - Lego Batman - Res Evil 5 - Trials - BFBC 2 - A's Creed 2 - Harm's Way - Crash Course - Alone in the Dark - Sniper GW - Kingdom for Keflings - World of Keflings - Deus Ex: HR - MW3 - Need for Speed: HP - Brink - Trials Evo - HAWX 2 - Mass Effect 3 - Op Flash DR - Minecraft - FEAR 3 - SSX - RSV2 - You're In The Movies - Halo Reach - Res Evil 6 - Dead Space 2 - Dead Space 3 - Dishonored - FarCry 3