Ok, I've got the official beta and a Trillian account. Astra surely is a thing of beauty. The UI improvements are nice and as a long-time Trillian user, they "feel" right. It does load faster than Trillian 3 Pro did (thank GOD!), though there are clearly still some performance issues on my 3 year old P4 running XP. I'm betting that there are still tweaks to be had.
As Sparks noted, many of the performance issues will be related to the skin you use, and I'll test that out more thoroughly throughout the week.
I've begun capturing some screenshots, and will give a full report on my intial testing this Friday.
Click the thumbnails for a full-size image.