I must admit that I never used to finish my seams. At all. If it was an especially fray-friendly fabric I would pink the seam allowances, but usually at the end so I would have awkward gaps as I got close to intersecting seams.
With Kasia, and the (supposedly) quick-y project I'm working on right now, I've been finishing seams. With Kasia, I used bias tape to make bound seam allowances. I'll admit though, that I did some of them at the end, so I need to finish the bias tape by hand, which I haven't done yet.
The dress I'm working on now will be a combination of bias binding and french seams.
I haven't give it much though before. But, I've traditionally only sewn semi-formal wear and almost universally under an absurd deadline (like, I need to wear the dress the next evening...). In cases like that, I simply don't have time to finish the seams like I should. But now that I'm sewing for long term wear, I think that it's worth the extra time to make the garment look that much better, and last longer.
Do you finish your seams? What method do you use, and how do you decide?