I tried to update to the cvs plugin 2.0 today but this doesn't work, I assume there is a name problem due to the extension *.jpi on the new plugin.
Before update, the file is called cvs.hpi, the update process creates a new file cvs.jpi that is ignored with the following message:

Jan 30, 2012 5:04:26 PM hudson.PluginManager$1$3$1 isDuplicate
INFO: Ignoring /home/lehmann/.jenkins/plugins/cvs.jpi because /home/lehmann/.jenkins/plugins/cvs.hpi is already loaded

I assume it may work if it were the other way around.

The version displayed by the plugin page remains 1.6 but there are a few exceptions in the log about missing classes like this

java.lang.NoClassDefFoundError: org/netbeans/lib/cvsclient/admin/AdminHandler

these classes are included in the cvs.jpi zip but that is not used.

I was able to fix the update manually by copying cvs.jpi to cvs.hpi, which resulted in a pinned plugin 2.0, but the automatic process has to be fixed somehow.