One of the main advantages of Linux is that it can practically run on any computer, meaning, that you can extend the life of an old computer. Linux can run with low memory and hard drive requirements.
I feel that Ubuntu is going against that. I have an 8-year-old desktop, with a AMD Athlon 64 bit processor, 2 Gb of RAM, and a ATI Video card with 256 Mb. Since Ubuntu 11.04 Natty Narwhal, moved from GNOME 2 to 3, and started implementing the Unity Shell on top of it, the PC started to feel slow, not responsive, glitchy. I kept upgrading to versions 11.10 Oneiric Ocelot, and then to 12.04 Precise Pangolin. I tried both 32 and 64 bit versions, but the symptoms of slowness, were still there.
So I started to look for alternatives, first was Linux Mint Maya, downstream distribution from Ubuntu. The advantage is that it offers the alternative between GNOME 2 and GNOME 3, but still it uses a shell on top of GNOME 3 to make it appear as 2, the performance was not there, and it felt stuck in the past, for me, Mint is just a cosmetic makeup of Ubuntu.
Then I tried Fedora, the open distribution from Red Hat for desktops, and it was direct, my graphic card / processor / memory, wont give me the full GNOME 3 experience, so it wont install. I think it could, but some serious tweaking would be needed.
At the end, it was OpenSUSE 12.2 Mantis to the rescue. SUSE is a downstream distribution from the old reliable Slackware. It’s a full Linux distribution with GNOME 3, and it runs like a charm, no lagging, no slowness. Lots of software from the repositories of the community. I think I will stay with OpenSUSE for a while.