I'm beginning to desire an entry level / used d-slr camera, and I hope someone can point me to a model to consider.
I'm a novice photographer, at best. no, I'm not even a novice photographer, I'm one of the people that they make point-and-shoot cameras for.
my budget is ~500 $us, so maybe I should just wait, but maybe not?
can anyone recommend a decent camera to cut my teeth on?
I'm guessing I'm better off with a used solid unit, rather than a new cheap one. but again, I really don't know all that much (read : nothing) about them.

I read an older post about a 30d deal, and all that I could gather is that there are people here that have a good deal of experience.

With any D-SLR, there's a modest concern of which system you're slowly but surely locking yourself into. If you buy Nikon or Canon, you've got an impressive after-market of used equipment. If you buy anything else, things get a little rougher.

That said, Nikon's bottom-of-the-line D40 cuts one very specifically important corner. All but the newest Nikon lenses expect the motor that drives the autofocus to be inside the camera. The latest Nikons have the motor in the lens, so the camera only needs to supply power. Part of how they cost-reduced the D40 was to remove the in-camera autofocus motor. This may not actually be all that big a deal, since you can learn your way around the D40 then upgrade later to a fancier body, should you be so inclined.

Alternately, you can consider the used market, where $500 should be enough to get a Nikon D50 or D70 plus a reasonable starter lens.

You forgot some of the other pros for the DSLRs.

Pros:

A real viewfinder, faster operation, faster response between pressing the shutter and taking the shot, typically longer battery life, holdable by people with big hands, thanks to low noise can take flash free shots when prosumers don't have a chance.

P.S. the DMC-FZ50 doesn't really have a 750mm 21x zoom, it pretends to have one by cropping the image to give the effect of zooming beyond the 420mm of the lens. You can get the same effect on any photo from any camera by just cropping it.