That's a very hard question to answer....and we've had mixed reports. Many say it's less resource intensive, while some have seen increased resource usage.
I can say we've identified a few "issues" in 3.0.0, corrected for 3.0.1, that can cause excessive resource usage in 3.0.
1) Sessions weren't clearing if you use PHP 5.1. This causes the sessions table to continuously build up, which slows things down. We've fixed the shutdown function registration to support both 5.1 and 5.2 in 3.0.1.
2) If you watch a lot of topics, or auto-subscribe to topics you reply to for example, this could cause the board index to slow down with the watched content hook installed. We've added a limit in 3.0.1 to the query.
3) The queries run on the portal were a bit slow. Optimized for 3.0.1 and a patch released in the customer lounge.
4) The view new content queries were rather slow. Optimized for 3.0.1.
It all depends on how many people are online, how much data in your database, which features are enabled and actually used, etc. :) Overall, you probably won't notice a huge difference either way, unless you run into one of the aforementioned bugs.