I keep 10.04 Lucid Lynx LTS around for things that don't work on Oneiric like:
Wireless on this IBM T40 Thinkpad. Connects with Narwhal and Oneiric, then disconnects a minute later. Yes there's a launchpad bug entered, however my wireless setup skills aren't up to the task.
Ocelot "Browse Network" is marginal at best on three of my four test pc's. Works fine on my Aspire 5253 notebook. All four set up identically, and works fine on Narwhal on all four.
I'm bouncing back and forth between Narwhal and Ocelot comparing them. Likely I'll replace the Narwhal with the totally unstable Pangolin .... and still keep Oneiric and 10.04 Lynx for what doesn't work on the newer ones.