I made several attempts at updating to IPSW 2.0.1 using the brand new Pwnage tool. Everything worked except Cydia would crash on launching. Tried loads of different ways but nothing worked. I've read other people having the same problem.
The way I solved it was to unzip the "PwnageTool_2.0.2.tbz" file again but this time forced it to be unzipped using the system Archive Utility rather than my normal unzipper (The Unarchiver). There is a mention of this on the Dev Team's blog but as it only says "don't unzip with a command-line tool" so, um, I ignored it as I've never had problems with The Unarchiver tool before (which is why it's my default unzipper).
Anyway, with the newly unzipped Pwnage tool, I rebuilt the IPSW and restored (DFU) and now it works perfectly.