Well it's not here yet. The phone was just released the 15th, and mine was shipped UPS Ground directly from their offices in Louisville Kentucky. I should have it sometime middle next week. I'll be sure to follow up with some impressions when I have it in my grubby little paws.
All the reviews I've read and watched indicate it's definitely way better than the Behold II, which is better than I expected to get from T-Mobile. 1ghz hummingbird cpu, 4" S-Amoled WVGA screen, 512mb ram, 16gb internal, 2gb microsd with that stupid Avatar movie on it (will be one of the first things to go lol). Touchwiz 3.0 seems smooth as glass and less intrusive than Touchwiz 2.0, but I'll likely revert to ADW.launcher unless the Samsung widgets captivate me.
And the phone has already been rooted lol. So no matter what people might end up thinking about the Vibrant, it's still a massive improvement over the Behold II. So long as it makes phone calls without locking up, and does everything the reviews suggest it does extremely well, I'll be content in all likelihood.