I have done it every time since they first offered it. I like the idea of already being "checked in" 10 days before. I don't usually have any room requests, which seems to be the big dividing factor between those who do and those who don't. So far (knocking on wood) my room has always been ready and waiting when I arrived. My arrival times have varied from as early as 10am to as late as 4pm. It does seem like it takes less time at the front desk because they just confirm your dates, # of nights, and the credit card you are using, check your ID, and you get your packet.
If you do have specific room requests, there's nowhere to note them on the online check in - so it is probably better to wait and check-in in person.