Why is Adobe Media Encoder so slow? I have a 2.5 hour corporate event that I edited in Premiere Pro. There are AE clips, sound, imported video, the works. When I run it out to AME, the source resolution is 1440x1080 and I am downsampling to 640x480 for delivery on Vimeo.

The thing is... Media Encoder is teling me that it is going to take 20 hours to render this video. Why would it take that long? I rendered last night at full resolution, it took 8 hours and produced a 27 gig MP4. I have run out video this size (previous events) with way less of a time investment. Clearly I am doing something wrong! My newbie-ness is showing something bad here.

I am on a Mac Pro, 2 x 2.4 GHz Quad-Core Inel Xenon tower with 22 GB of RAM running OS 10.8.4 and the Adobe Master Suite 6.

Can you make a suggestion, or maybe point me at a tutorial on render settings? I thought I had everything set right, but this is crazy!
10 times the length does sound pretty long, but isn't completely insane, particularly if you are running two pass.  The more compression you are trying to do while maintaining quality, the longer it is going to take to compress it down.  

It's also possible that if you are using nested projects, it may still be trying to do some rendering at the native resolution of the output for it.  Are you running the MP4 or the project through encoder?  If you have a full res MP4, I would suggest trying to run it directly instead of running the project.  The quality will likely be lower, but it should run a lot faster.