Looks pretty good, Quik. I attached a very poorly drawn picture, but if you
really want to get rid of the tris you could go for another loop around the thumb like something in my paintbrush masterpiece...
(the quads are a little skewed, but I think you could tweak them to get a better effect.) Personally, I don't think it would be too much of a problem, it just depends on how it deforms for animating and such. I would shorten the thumb, however. It looks a little out of proportion.
Also, you don't have to add any detail for the wrinkles on the fingers, but I think if you plan on animating or rigging this hand, you should have some polygons that can collapse. It will add a little control to the skin.
Take a look at this pic.
Edit: you beat me Kira Vakaan! But that's okay. Yours is a much better solution. I guess I shouldn't take so long to type.
My green thumb grew the tree my Trojan War horse was crafted from. With roses in our pockets we rally round the tombstones. Ashes to ashes, we all fall down.