I've heard a lot of good things about Rose::DB and DBIx::Class, but unfortunately do not have any real experience with either.

However, I do have a good deal of Class::DBI and Alzabo experience. Although, Class::DBI has its limitations, it works well for simple designs. On the other hand, Rose::DB is faster and I've heard DBIx::Class is basically Class::DBI's 'replacement'.

I don't really hear too much about Alzabo and it seemed like a somewhat elegant framework and can be a little more involved than your typical ORM. It keeps a cache of your schema, which means changes require a reload. I've built some cool applications using it. I cannot attest to its scalability, however. The biggest app I built with it was on the low-to-mid size, but worked like a champ.