I think Pena will stick in Atlanta, and I've posted my reasons for thinking so on O'Brien's blog.
I've also posted a copy on my stupid fansite, but it's too long-winded to just copy and paste. The gist of what I said about Pena is that he's too versatile (a switch-hitter who can backup for 5 positions? please) to let go. He doesn't do anything spectacular, but he does
everything passable, so it's like having more than one player in only one roster slot.