You can build a high-end desktop with top of the line everything, including a 4x or 8x DVD burner, and anything else you might want for processor-intensive operations for $2500 and use a $2.2K (both figures USD, not Loonies) Thinkpad for lugging around. (Not that I'm doing that... I'm getting one of Bills incoming top-end T42ps). People who are used to the 4x or 8x burners in desktops will be shocked at how slow the 2x burners that come with the T42 will seem.
I do wonder whether ANYONE has ever had to burn a DVD on the road. Since I started lugging CD burners around (in my A21p, I think) I have had to burn exactly two CDs when I was traveling, and now that there are USB2.0/firewire portable HDDs I doubt that I would have to burn CDs on the road-ever. Someone to whom I wanted to transfer big files would take them off the external USB2.0 HDD, although I suppose that there are company adminstrators who use group policy to stop road warriors from accessing external HDDs but not DVD disks.
Anyway, in a gesture of fiscal rationality I am not having my firm buy me the DVD burner in my new T42p and am getting "only" the CD-RW/DVD-ROM optical drive, saving $200 before Bill's discount.
Probably burning dvd for backups only, when you have a large files.
As for cd-rw/dvd combo II, it is faster than the DVD-RW drive, for both reading and burning CDs.