It takes a long time to access my achievement list and marketplace from my console. I was able to solve this by formatting my hardrive, clearing cache and recovering my profile. Unfortunately the problem came back within a week.
I found that tranfering my profile to a USB storage device solves the problem but again this is temporary. I'm currently transerferring my profile back and forth between a USB stick and my hardrive whenever this issue occurs which is less than ideal. Any ideas on a permanent solution?