Sounds similar to what I was thinking. I was just not sure if there was some unforeseen gotchas that others had dealt with before. The move to a new version is usually not that bad but I knew moving machines with versions could be hazardous. I may end up upgrading the local copy to 2.0.9 before the move so they will be similar.
Perhaps, but did you not like my suggestion that you could have basically both versions live at the same time?
To recap, rsync (etc) some data across to the new server which has been upgraded to dovecot2. Set proxy to forward some test users to the new server. Test it thoroughly, copy over a few more accounts, repeat testing, etc
This keeps both old and new servers running at all times and the "proxy" feature allows you to push users across even one by one (or do a bulk move).
Remember, apart from the slight gremlin that the dovecot index files get made non v1 compatible by the v2 server, the data can be copied back/forward between servers and most MUAs will likely not notice the difference between your v1.2 and v2 installation... Don't get over-fixated on the server version, focus on not ending up without a working server during the process
Good luck
Ed W