I believe that, if possible, you should get a few dives done with your OW cert before moving to AOW, mostly so that you have some comfort level with the simple tasks of diving before you move on to the heavier task loading of night dives, etc. in AOW.
I do think there are notable exceptions to this. Divers with experiences like Ali's, who feel they need additional help, can get refreshed in the basics while they are taking AOW. I don't know how the instructors on this board feel about that.... essentially, they would be reteaching some of the OW course as well as teaching the AOW information/skills. It's valuable to have available, though. I know a diver who came to my LDS from a poor OW instruction environment who actually asked on the dive boat, "What's a safety stop?" That kind of diver should have additional instruction available, and I don't think many divers are as realistic as Ali in that situation in considering actually retaking their OW class to get whatever they missed due to poor instruction originally.
On the other hand, I took AOW with a diver with had literally never been back in the water since her OW cert was completed. She had taken good instruction (had been in my OW class), but simply showed a lack of familiarity with her own gear, was not comfortable in the water, and had never addressed the fact that she was worse than legally blind without her glasses. I privately took the instructor aside and told him that as a diver with only 19 dives to my credit, I did not feel comfortable buddied up with an incompetent diver like that, especially not one who would be having to try all kinds of new things during the dives.
I guess, when it boils down to it, I feel like you need to get out and practice what you learn before you take on more information. How much you need to practice it is going to vary from diver to diver, but if the only experience you ever get in the water is what you get diving with your class, you won't get enough practice to ever be comfortable with the things you've learned.
Julie