I try to find a compromise between doing all thumbs by hand and using Arles. Let's take one of the sample galleries Ramster posted as an example.
http://www.nshoneys.com/hosted1/hc/f....php?id=100031
I would still use Arles for this gallery, but I would have set the thumb size such that the watermark in the lower part of the image would have been cropped, which would have also cropped a little off the top. I would still need to go back and manually thumb images 7 thru 10 to get more girl and less bedspread.
That said, the focus of most of my galleries is stockings & heels or boots, so I want mostly full body shots rather than focusing on big tits, not that I have anything against big tits.
I'd say that about a fourth of the time I make all the thumbs manually, a fourth of the time I use all Arles thumbs, and the remaining half end up with a mix of both.
It's all a matter of ending up with nice looking thumbs that are going to make your galleries more appealing to your target audience than the galleries of your competitors.