Actually, I just ordered an 08 ST about 2 wks ago, and I was all set to buy the Ridgeline. Then I test drove them. Totally different ride. Others already mentioned some of the things that would be on my list which are:
-the bed of the Ridgeline is so high it's difficult to use. The high sidewalls also make it kind of difficult.
-no V8 option for Ridgeline
-visibility is much, much better in the ST
-the Ridgeline has an issue with clearance. The Edmunds test drive talked about the horrendous noises coming from underneath when they took it off road. I heard those horrendous noises going into the dealer driveway (I did not clip the curb--seriously, it scraped over ~2inch step up).
-no MP3 on the Ridgeline unless you get the Nav system
-styling (although I don't think the Ridgeline is awful, I just like the ST better)
About the first order date, one dealer told me they started July 12th. At any rate, you can order now.