I just started using Rockbox on my Clip+ and it... well, rocks.
One feature I would love is that ability to pre-specify a start and stop recording time. For me it means one less thing to think aobut when I'm giving a presentation and want to capture what I say (since I'm usually not paying a lot of attention at the time. I already have this feature in some dedicated and expensive digital voice recorders I own. However, having it here means one less thing to carry.