While I said quite early on that I had Ubuntu Feisty running in 64-bit, it wasn’t until today I got things really how I liked it. My earlier Perl problem was due to a broken gcc setup; all is happy now, and all the modules I’ve ever used are built and running as expected.
The one thing I’ll probably never get going is Citrix Metaframe presentation client. There’s no AMD64 package for it. I’m hardly heartbroken, as I still have two machines on which it runs just fine.