I was curious what kinds of obstacles have you encountered when migrating my app from seam 2.0 to 2.1.
Obvious ones are mentioned in: migration guide, but I encountered some problems with rule based security, that are not mentioned there.
Firstly I want to post descriptions of my problems and my solutions with migration, so people can benefit (I did'nt find any solutions on the web) --- i'll post it as an answer :)
Secondly I would like to ask you what problems you had when migrating, and how you solved it, so it is in one place in the web.
As already mentioned the security handling has changed (see migration.txt in Seam distribution).
Furthermore the build architecture has changed massively. If you use the generated build.xml you should regenerate it and manually redo the changes you did. The same goes for some other build related artifacts, some files are now profile dependent and deployable libs are specified in deployed-jars-ear/war.list. The easiest way is to do a merge between two generated projects, the changes are pretty obvious this way.
Other than these two I did not have any problems upgrade from 2.0 to 2.2.