Just an idea from me... OK, rather than a register of sorts, would a "My Garage" not be a more personal way to go? Calling it a Register seems a bit out of fashion/date
To me the concept is perfect but need more personality so what about a searchable "my garage" which could consist of:
Expense tracker (If you dare)
BHP and Torque
rolling road graphs
People could tag your car in images (Like face book
Servicing reminders - For instance you could be prompted to input your mileage every month, this will track when your service is next due (because you already set the mileage etc at first use)
Track MOT, Insurance etc...
If VIN plates are used then we may be able to tap up Alfa for a feed to recall information, after all this may of stopped the recent MiTo problems more quickly!
Any how thats all I thought of in 5 mins, there is so much we can do for sure, but we do have limited resources when we talk about development, soon we may be able to announce something that will help get this off the groun more quickly as we may be able to out source it as we have so many projects on at present/pipeline. We do want to give you what you want so I would be interested in much more details or ideas.