It'll play DVD-Rs fine but if I remember correctly, it doesn't like DVD+R discs unless they're bitset to DVD-ROM.
I can't remember if the N501 likes rewritables or not. (When I got my first DVD burner I went through everything I owned to see what worked and didn't but that's been a long time..)
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.