A few days ago I bought a larger and faster disk for my Dell Precision M65 notebook. If it wasn't for the new disk, I would have never tried the latest Ubuntu (13.04, aka "Raring Ringtail"), because 12.04 worked fine for me. Feature-wise I haven't noticed a lot of new stuff, so if you're happy with the previous version, stick with it, it's an LTS which has support until 2017, while 13.04 is only supported until early 2014. Anyway, here's my first impression.
I did a fresh install of the 64-bit version from a USB drive because which worked without any freezes (unlike last time). Without the binary driver for my G72GL Nvidia graphics card, Unitiy wasn't usable though (I ended up using the nvidia-current-updates package). Suspend and hibernate didn't work out of the box, dmesg(1) showed "1 tasks refusing to freeze". It turns out that I had to get proper firmware for my Broadcom BCM4311 wifi chip first. Like last time, I tried installing the b43-fwcutter package, but the automatic installer is now in firmware-b43-installer, so I had to use that one instead.
Ubuntu 13.04 doesn't provide the deprecated libudev0 library anymore which is required by Google Chrome, so I had to install it from 12.10. The Google developers are working on a fix though, so that workaround won't be required if you can wait for a few more days.
Installing Maven didn't work due to a broken package. I had to force installation of libwagon2-java. The Debian-specific Java mess is a a topic on its own, I'll post a new article on that soon.
Out of curiosity, I clicked the "encrypt home folder" during installation. As a side effect, the swap partition got encrypted, too. This makes sense when you think about it, but it breaks hibernate support because the system can't resume without a key. There are workarounds for that (you'd have to enter the key before resuming and it has to be the same for all users), but I didn't have the patience to solve this, so I went back to an unencrypted home directory.
Other than these small hickups, most of which weren't Ubuntu's fault, this was a rather painless experience. Two colleagues of mine who upgraded their systems weren't so lucky though. One ended up going back to 12.10, the other one decided to tough it out and is still struggling with all kinds of problems. Again, my advice is to only upgrade if you have serious problems with the version you are using (or support has run out).