The captivate I had, you could change the battery in well under 5 seconds. Bootup time was longer but not really any issue since typical use case was not to be using it immediately after.
Now I have a Razr Maxx. I was concerned about not being able to change the battery easily at first but it really typically has enough capacity that it's rarely an issue. It has been a pain how long it takes to charge on a couple of occasions though.