Yes, the new Ubuntu is nicer...than previous Ubuntu versions. Got it installed on a VM and set up a clojure environment, which is a pain the the ass on Windows. Still can't wait for Windows 7 to come out though.
Nice! Why not run a more striped down version of Linux for that clojure environment? Ubuntu is pretty fast, but it still uses a lot of RAM compared to, say, puppy linux.
Ubuntu is more widely supported, and I have 8 GB of RAM. I don't know if using less memory is worth the effort to learn something new. For instance, I rebuilt my dad's PC with an Atom CPU and 1GB of memory and installed Ubunutu on it. It works great. I might give puppy linux a go on my netbook though.
Straight Debian is much like Ubuntu, but without the weight.
It's much easier to get it down to a minimal size for VM's (I know a guy who made a tiny version, with barely enough in the kernel to boot.)
Yup. I just did an upgrade to Jaunty and it has been very pleasant.