This is a chime-in for the issue reported by LenFeldman sometime last April. I recently started modifying my blogs after some time-off and noticed that Google Analytics suddenly flat-lined after updating to a newer template/theme. It seems all the code got lost during the process. That means, like him, I've lost months of tracking reports :-(
I've put the codes back manually with help from eBlog and will be monitoring my sites this week. Hopefully everything goes back as well as the new site going live successfully.