Reps are not always the most reliable source of information. Recent rumors of firmware issues may be a slight hitch. My bet is an EU release in Oct/Nov and a US release between Dec 2009 and March 2010. AT&T will do the same thorough testing that they did with the Bold.
I'm a mobile phone OCD poster child...and I'm looking forward to the Onyx like everybody else...but I'm pretty ok with it being released later in the year. I like my Bold, and don't see so much difference with the Onyx that I am ready to throw my current device down and jump on something new.
Faster processor, more onboard memory (albeit not much), improved camera (wouldn't take much), and a little more svelte design...? The Onyx will be an improvement over the Bold, but nothing earth shattering. But then again...the Bold doesn't need much improving IMO.