I Own both. Cubase was my first "real" DAW and I used it for a few years before investing in Pro Tools. I upgraded to SX2 but haven't been able to justify getting 3. I just don't use it all that much.
Pro Tools does have wicked fast editing, and I like that most eveything happenes with the 2 main windows. It also comes with a few plugins that I like better than the stock Cubase plugs. Pro Tools LE and most of the RTAS plugs don't have a delay- not like the TDM system plugs which ALL have different delays.
I *really* like being able to move projects from studio to studio with Pro Tools- that actually lets me work: Pro Tools may not actually be any better than the other programs out there, but it does have name recognition. I've paid for my Pro Tools with the work it allowed me to do.
Cubase has:
Unlimited tracks, full dealy compensation *even* on hardware sends(!), timecode and advanced video functions, OMF inport and export, faster than realtime bounce, track freeze, distributed processing... the list goes on.
Pro Tools: cheaper to get into at the ground level. The mBox comes with PT and is less than Cubase SX. While this is true, the arguement breaks down when you realize PT LE is more on the level of Cubase SL.

Verye expensive to upgrade.
Cubase: Infinitely upgradeable and grows to the limit of your hardware.
Seriously, the only reason I chose PT over Cubase is because of the professional work that I do. That's the only reason I'd recommend it to a home recordist, as well, because Cubase pretty much kicks its butt in every other area except work flow.
Take care,
Chris