According to some posts across the web, there are a few users that have experienced major issues with the new Ice Cream Sandwich update on the Transformer Prime. According to a lengthy post over at XDA, a small smattering of users are having lockups and reboots after updating the device, regardless of whether they have rooted or not. In some cases it makes their tablet completely unusable.
Unfortunately, at this point, Asus support is stumped by it, and there doesn't appear to be a fix yet. Even a full wipe has no effect. This may only affect a small number of users, but it is something to keep an eye on. Let's share in the forums as new info arrives.
Source: TransformerForums via AndroidPolice