I have been making short (5min to 10min) movies for the web for several years. I have used Premiere Pro CS3 and exported to FLV using the CS3 Adobe Media Encoder. The results have been excellent using 800kb/s at 25fps.
I then upgraded to Premiere Pro CS4 but cannot get anywhere near the same quality out of the new Adobe Media Encoder. I have tried many settings, including 2-pass and/or VBR as well as Single Pass CBR. What ever I try the resulting video quality is poorer than from CS3.
For the moment I am sticking with CS3 until I can find a solution. I hope I have not wasted my money on the upgrade.
I have found in my testing that the Flash encoding options and the results are far superior to anything I ever got out of previous versions of this option in PPro CS3 and v2.0.
That being said, I always use Sorenson Squeeze. Wish Adobe could match the quality I get in Sorenson. It's closer than before, but the file sizes are still much bigger in AME and the quality is noticeably lower than what Squeeze can deliver.