My son is 4.5, and he's been more or less potty trained for about a year and a half. Except for two things:
1) He still has pretty frequent accidents. Usually it's just a little bit of pee, and then he realizes he has to go and runs to the bathroom, but he's got a wet spot on his underwear, sometimes on his shorts. We've tried to deal with this with rewards (candy/quarter/sticker on the chart every time you have dry underpants) and it's been reasonably successful, but we also remind him to go a lot. He starts kindergarten next week and I don't think they're going to be as diligent about making sure he pees as we are!
2) He's leaking through his pull-ups at night. He's a heavy sleeper and really nowhere near night trained - he's never woken up at night to tell us he had to pee. But lately he has been waking up at night because his shorts (and bed) are wet! It was happening on a very regular basis earlier in the summer, so we went up a size in pull-ups and started making sure he peed at bedtime and then taking him to the bathroom again when we went to bed. It worked great, he was waking up with a dry pull-up. Then it stopped working but there were still no leaks, then we got lazy about it, now we've had two days of leaks again (and last night I did limit what he drank at bedtime and tried him on the toilet when I went to bed).

We're using Huggies Pull-ups 4T-5T - I'm open to changing although I'd prefer not to, because we already have an unopened box of 3T-4T, an unopened box of 4T-5T, plus 99% of a package of GoodNites that we tried once before realising they were enormous on him (he's really small for his age, weighs about 34lbs).

Does anybody have any advice/commiseration on either issue?