This summer I took my Dell Latitude D830 with me on holiday to view the movies that I recorded with a Panasonic HD video camera.
Frustratingly enough, in France it turned out to be impossible to play them on my laptop 
Spent hours fiddling with every imaginable setting. At home everything worked fine though.
Yesterday I had packed my stuff to go watch a movie at a friend’s house, and when checking the downloaded MKV again I noticed that VLC had huge problems playing it, both 720p and 1080i H264 files.
Everything started working when I accidentally swapped power supplies. Turns out the D830 (maybe other models too) severely slows down when you use the small 65 Watt power supply.
Tip: ONLY use the 90 Watt model, unless you want to experience Pentium 4 speeds…