Ok, I'm making the plunge into burning my own MP3 CDs (in data format, not CD format)

My question is this -- If I make a CD, do I have to take all the MP3s and put them in the root directory, or can I leave them in the subdirectories that were created when I ripped the CDs? (Yes, I'm actually ripping CDs I own)

It depends on what your player supports. The smart ones can traverse directories and play .m3u files (playlists).

Any examples of 'smart ones'?

Well, I have the rio volt sp250...I have each album in its own folder.

However, I don't think you can have folders within folders...if you know what I mean.

Btw, I love my mp3cd player. I've ripped pretty much my entire collection and was able to fit them all onto about 25 mp3cd's.
I'm now able to carry around my entire collection in just a small little cd case.

I have the Rio Volt Jr. and it reads folders. I think most of them do nowdays, if it was released in the last year or so.

It will play folders within folders, but it won't autodetect them. You will have to manually navigate to the lower folder.