I decided to connect the Ubuntu 6.06 LTS (Dapper) drive today, and I've spent quite a bit of time using it for work. Now this isn't the highest-spec machine (only 256 MB of ram, 1 GHz processor), but it's doing pretty well.
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Final question you might be asking: Why Dapper? Why not Feisty? Well, I think the LTS edition of Ubuntu is important — not everybody wants to upgrade all the time — and I already have the drive set up with 6.06. I have worked a bit with Xubuntu Feisty (that's the version to which I'm comparing Ubuntu Dapper), and I've just wanted to keep this LTS setup around.