Matt Laur , Nov 20, 2008; 02:31 p.m.
It comes down to:
1) Horsepower. An AB800 will give you a couple stops of light that the SB800's can't. And they can recover from a full exposure over and over again, and quickly... and with less wear and tear than such use would cause to the speedlights. You'd also be able to use larger light modifiiers with the ABs... but that brings up the issue of what you're shooting (say, a bride and groom, vs a group of 30 people in a big dark room).
2) Flexibility. Presuming that your shooting circumstances will allow the D80's pop-up flash to control two remote SB800's using Nikon's CLS, it is sure handy to be able to control the speedlights from the camera. With the AB's, you'd be walking over to each of them to adjust power (unless you use the wired remote widget). With Nikon's CLS, you can adjust the remote strobe power from the menu on the back of your camera - quite cool.
But, about the CLS... there is always the lag time introduced by the pre-flash necessary to communicate with and fire the strobes. You can get around that by using Nikon's infrared controller, but that's almost as expensive as yet another strobe... or even some decent radio controllers.
The speedlights would actually be the easier of the two to set up, under many circumstances. No power cables to secure, no power outlets to find, no synch cords or radios. But you're only as good as the batteries, and the reliability of the optical triggering. Of course, you can use radio controllers with the SB800s, too... but you lose the CLS/iTTL brains.
Or, consider that these things are not mutually exclusive. You can make immediate use of a second SB800, and later - if you get into beefier monolights - still integrate those SB800s into a more standard lighting configuration. If you put an SB800 into SU-4 remote mode, it becomes a simple optical slave, and can be triggered by one of your later ABs going off.
Regardless... if you're starting to do events, you really should have two speedlights no matter what. What if your first SB800 were to fail? For bounced on-camera light right off your D80, an SB800 is hard to beat... unless it dies. So, just like you should have a backup camera body, you should have a backup speedlight anyway. And when everything's working right, you've got two light sources for mobile use. But you've got to be realistic about how much light two SB800's can actually generate when you get into larger scenes/groups... at which point even two AB800s may not do the job, either.