Tommy - from 5 years experience with board sigs - I can guarantee you that it is worth it
Now relying completely on sigs for all of the backlinks will not get you that much - but - like the old saying goes - every little bit helps
For those of you worrying about what your PR number value is - where the fuck do you get the idea that you know what number PR your page really is - there is no way (outside of working for Googleplex) right now to calculate that value - and I hope you are not using the toolbar to tell you your PR of a page - if you are - youve got a lot to learn grasshoppers