Well, my son is only 3.5, but he still wears diapers at night because he doesn't wake up dry, either. Partly I think it may be because he is wearing a diaper. He knows that if he has a diaper on, he can just go, but if not, he has to run to the potty. I have friends with children my son's age and younger who've bee night trained for a while and they just stopped putting the pull-ups on. Because I don't want to deal with changing the sheets at night, I am planning to buy these covers that go across the bed over the sheet, so if they have an accident, you just change the "sheet saver" (buy 2). I found them at http://Health-Products.drleonards.com/Health-Products/Inc...
and http://www.collectionsetc.com/Item58172.aspx?WT.mc_id=3DZZZ5
I was looking for queen-sized, as that's what my son sleeps on- twin is actually easier to find.
Just a suggestion. I'll try to remember to let you know how it goes when we try it out. Obviously, we'll have to change pjs at night if he has an accident. Hopefully he'll wake up, but you never know.