What causes this, and is it common? If you let it sit a day or so, when you first crank it, it smokes just for a second. Not very much, but white enough that you can notice it.

Possibly needs new valve stem seals.

Pure white? ...or is it blue?
It's common for the exhaust valve seals to fail early from heat, but oil typically burns blue. Are you noticing any oil consumption? If not, it could be condensation in the exhaust. What's your weather like right now - is it cooler in the mornings?

I would toss some oil treatment in there.  If it fixes it, all is well.  If not it probably didn't hurt anything.  We put some Lucas in my brothers Tracker and the early morning puff of smoke disappeared completely.

Sounds like my daily driver Tracker with valve stem seals leaking, like Rhinoman said.  Mine has had it for years, about 50K miles now.  But if it bothers you, fix it.

Thanks guys. Are valve stem seals expensive to replace?

Lilred, sounds like yours isn't causing any problems. It doesn't really bother me, I just wanted to make sure it wasn't gonna cause any damage or anything to let it go

And I think I'll try the oil treatment just for the heck of it

Yeah, that's what I meant, that it wasn't something you had to fix immediately, unless it just really bothers you.  If I recall, it wasn't very expensive.  I just tend to spend my money on parts for the trail rig it seems!

Valve stem seals would be my guess too.  I have a couple of sidekicks that do the same thing.  Hasn't bothered me enough to do anything about it.
I don't think they are really too expensive, just kinda a PITA to replace.  You have to take the valve springs off (which means you need to compress the springs and take out the little tiny keepers and hope you don't drop one down the oil passages in the top of the head).

haha. I agree there lilred!