Like many others I like to generate signitures of functions I've RE'ed in a target so I can apply them to an update.
There are a lot of issues with the process.

This is yet another IDB2Sig/IDB2PAT plug-in for IDA Pro with some improvements to help with some of the problems.

Instead of relying on broken function types/tags, this uses function name text patterns.
Easier to go from one IDA DB to the next for updated targets, easier to update function names, don't have to combine multiple .PAT files, etc.
And as fast as TQN's version with out the huge buffer.

While IMHO this is an improvement in the process, but it certainly dosn't solve all the problems.
I think a whole new project is in order, something that will replace ".sigs" for update processes..

See the help file for more info..

http://www.openrce.org/repositories/users/Sirmabus/IDA2PAT_Reloaded.zip




https://www.openrce.org/blog/view/1242/IDA2PAT_Reloaded

CRCETL:
http://www.woodmann.com/collaborative/tools/IDA2PAT_Reloaded