For as simple a rundown as I could find, you might want to look at How to use a USB flash drive at Wellesley College.

(I was going to shorten the link display, but "how to flash at Wellesley" didn't sound quite right.)

Note down at the bottom of the page at "Notes and Cautions" the comment that you can probably use a flash drive interchangeably between PC and Mac if the flash drive is formatted in a PC as FAT32.

I don't know that any other format is commonly used on flash drives. You probably can reformat a flash drive, but since it's a USB device it needs to have "PNP identification information" on it, and a simple format by the PC may not save/recover the correct info for the flash drive to be recognized correctly. Most flash drives come with some small files preinstalled, and copying them off before formatting and then restoring them after the new format might be enough to keep them working; but I'd recommend a search for instructions before attempting it. The flash drive makers should have format utilities and instructions on their websites if they're needed; but I haven't had occasion to look for them.

The note also states that "not all files are compatible with both platforms." You should be able to save these files from Mac and back to Mac, or from PC and back to PC; but you won't be able to save from one OS and then save them back to the other OS in usable form.

Flash drives are similar to the memory cards used in some cameras and may have the same "formatting" difficulties." In the camera case, you should always use the camera to reformat the card. You can reformat one using the computer's format utility but it's unlikely to work reliably in the camera if you do.

I haven't heard of a limit on number of rewrites on flash drives, and some flash drives are commonly used with some computers as supplemental RAM, where they would approach "infinitely many rewrites." I'm dubious about this info. I have had enough "early failures" on a few flash drives to question their reliability as a place to put the only copy of critical info; but I think there were other reasons for those failures.

A very real limit on rewrites is well known for CD-R/W disks, but that's a rather different animal.

John