When answering questions for new members I try to offer the easiest method of reaching their goal, not hoping everything goes right, if and when.
But I understand your point that: sometimes....
With 7 it's not so much a shot in the dark as it was in older versions of Windows. Microsoft has officially started that Windows 7 was designed for this type of move.
It isn't going to hurt anything to give it a shot. I haven't read or heard of anyone having problems moving their HDD into a different system under Windows 7. In fact, I've read of some Computer Builders who install a customer's HDD into their system to clean/repair and then return it to the customer's system, all without a hitch.
When I moved my HDD from my Asus P5N-E to my new MSi P67A-C43(B3) I was greeted on boot with a long list of successful automatic driver updates and replacements... of course I had to go to the manufacturer's website for a few drivers that Windows simply used generic drivers for, but it was definitely problem free and very easy.