Today I decided to upgrade my HTPC from Ubuntu 9.10 to 10.04. (The Update Manager has been offering me to upgrade for a few months now)
I figured that, as 10.04 has been out for a while now, the little annoyances and bugs had probably been worked out and I should be able to run everything that I need (XBMC for MKV video playback). Turns out I was wrong. Never *EVER* touch a running system! You'd think I'd have learned that by now.
The upgrade completed successfully but it turned out that HD video playback of MKV files does not work so well with Ubuntu 10.04 on my Acer Aspire Revo AR1600. XBMC started fine, but HD video playback was choppy as hell.
I searched around a bit and while other people have the same problem, there doesn't seem to be a solution. I think the problem is not XBMC, but either Ubuntu or the Nvidia drivers in conjunction with Ubuntu. Either way, it's screwed up now.
I'm now backing up the files I need from the box to an external drive so that I can do a re-install of Ubuntu 9.10 and have everything just like it was 2 hours ago.