I've been thinking about getting a trackball, or a mouse-trackball. Also, something to take the place of the wasd keys, and I know there are various devices for that.
With flight simulators in particular, mice (and though I haven't used one, trackballs) are of course very precise but tiring to use.
It would be nice if there was a trackball that could switch between an analog mode, like the way a stick works on a gamepad, and precision mode.

Also, since I've never used a trackball, how good is a finger/thumb trackball? Is it best to just get the hand trackball or no trackball at all?

I don't think you could get a trackball to function as an analogue stick (if that is what you're asking), since there are no springs to 'centre' it. Also, I doubt anyone has written drivers that allow it to function like that.

Anyone have any experience with trackballs? Are they better than mice?

For most gaming? Definitely not. For emulating games that originally used trackballs? Nothing is better. For situations that provide minimal desk space? Most people would prefer it to using a trackpad or using a makeshift surface. Is it more comfortable? That varies on the person, but you'll more than likely need some time to adjust.

There are advantages and disadvantages, but overall, I'd say the mouse became the standard for a reason. Some people can use trackballs just as effectively, even in first-person shooters, but most of those people were likely raised on trackballs instead of mice.

As far as the analog mode, I can't really say anthing about that. I've tried a few things that work sort of like that with touch screens (The analog movement of some DS games like Super Mario 64 DS is a good example). I don't think it'd be especially practical, and I wouldn't know how to set it up to work that way, either.

I use a trackball with my computer; both for gaming and other stuff. I like it, but be aware that it takes quite a lot of time to get used to it. It took me several weeks before I really got the hang of it. I think the reason most people hate them is that they don't persevere. The learning curve is much steeper than it is for mice.

As to whether they're better than mice: I don't think so, but after getting used to them, they don't have to be worse. Maybe mice are still somewhat better for precision work, but a trackball has the advantage of staying in one place - you don't have to move your arm/wrist.

My wife uses them exclusively, I recommend thumb balls over finger ones for comfort reasons. If you have problems with mouses (I hate it but thats the plural of computer mouse -.-) I do recommend trying them as they cut down on a few of the major problems

Don't know if this would help you, but have you looked into "keypads" like the Logitech G13? I picked up a similar product a while ago (that's ambidextrous, since I'm left-handed), and it's really nice for FPS and RTS games. I remember reading somewhere that like DVORAK keyboards, they're supposed to be more ergonomically efficient, and less apt to promoting RSI injuries.