Ok, thanks for the answers - at the moment I'm looking for a VFP-only solution (for users without any server back-end: for the latter I should be able to piggy-back onto their systems). I'd hoped someone out there was using something...

FWIW:-
I came across www.syware/datasync which handles all sorts of databases but at the last incarnation couldn't handle BLOBs. It's almost ideal in that you can use any transport (e.g. dial-up, ftp, disk, e-mail) - I've asked for more info re: BLOBs but have had no answer yet.

Also found www.cntc.com which looks very interesting although more limited in its transport mechanisms.