Rebooting via killing the humaxtv process isn't very clean and I haven't yet confirmed whether it properly syncs and unmounts the disks so it could lead to corruption (although ext3 is journaled so it
should be safe). Otherwise the scheduling hasn't been widely tested and does no conflict checking at all, adding overlapping programmes could have undesirable effects which need investigating (volunteers?).
The next version of the webif that's in development adds the new programmes to a different database and the entries are synced across during boot, before the humaxtv process launches, which is much safer. It also uses a different technique to reboot the box.
It will also add a pretty funky remote scheduling feature that I think people will like