Very nice job. Intuitive interface, does what you want, and caters to slightly less trivial needs just fine.
The only gripe I have is that it stores serialized Perl structures as opaque text/BLOB fields rather than even attempting to store the data relationally, but that limitation also means it is very easy to get working and that it can store any data structure Perl can handle. So there is definitely a trade-off involved.
After creating my own website session management system, it was refreshing to find CGI::Session which encapsulates a number of the the 'harder' parts of the problem space into a simple and easy to use interface. The documentation for the module is excellent and thorough.
A number of databases are supported, including the possibility of using flat storage. This helps to make applications using CGI::Session even more portable.
My only complaint about the module is that it stores a big Perl data structure in a SQL data field, instead of storing the data using standard SQL techniques, which would allow more flexible access.
I've written CGI::Session::PureSQL to address this, which I hope to get around to polishing and releasing Real Soon Now.