For Divine Divinity I played it straight through (taking a break in the middle) once, after playing the demo (ie up to the first meeting with Zandalor). I started another character after that, but ended up getting busy with other things and abandoning that game.
D:OS, though, I restarted more than I needed to during the beta (saves were generally not compatible between updates). I'd like to get a full playthrough in the beta patch, actually, and have a different party makeup in mind for when the harder difficulty mode gets added.