Apart from the SQL upgrade script balking because of an old record missing from the cs_SchemaVersion table (I just added it manually) the updating the database went without incident. Upgrading the web application was slightly more time consuming as I had to merge my changes to the *.config files with the new versions but after that I just copied my custom theme directory across and then uploaded it to the server.
Now I just need to find a new blog feature in Community Server 2.1 that I will actually use to make the upgrade worth it [:)]
The admin area is much improved. Most the rough edges around the post editor and post grid have been smoothed out. Also the new "named" URLs are much better than the old number system. I went through and updated all of the previous posts to use them (the old URL still works).
Overall I give 2.1 two thumbs up [Y] [Y] (did I mention the smilies in blog posts? [:)])