Warning: anecdote follows.
I recently installed Ubuntu 9.10 on an Acer Aspire 3680, to use as a basic HTPC with Boxee. I was impressed with the overal finish of the OS and initially was glad I could use open source software. At least, that was until I tried to get s-video working, with either the laptop screen at native res, or the same res as s-video but in the correct aspect ratio (4:3 on 16:9).
After discovering that Ubuntu now believes Xwindows to be so good at autodetect that it no longer requires xorg.conf, and then wrangling with various configuration options for hours, I gave up, found the WinXP disc and had everything up and running in short order. No voodoo magic workarounds, no text file configs to create, and dual video output with native res on each.
TL;DR: Ubuntu's good looks and neat UI effects are fine, but when It Just Won't Work, people jump ship - fast.