Bloatware yes, my install directory for AP9 is almost 2GB. I really think they bloat it up to make piracy more difficult.
But this is interesting: I loaded Acrobat Pro 9 on my multimedia rig here (2.13Ghz dual core Intel, 4GB RAM, Vista with Service Pack 1).
Acrobat Pro 9 loaded in less than 1.5 seconds of my clicking it.
Looking at task manager, it takes up almost 16MB of memory on startup. Granted, that's without having a document loaded.
There was no acrotray.exe listed in task manager. I remember when that would be installed in previous versions, but now that I think about it I haven't seen it listed in Task Manager or my startup for some time... unless it's something else now?
For a point of reference, Firefox.exe had over 141MB of memory. That's after visiting here, and before that eBay, Facebook, and some other related sites with only having a single tab open.
I'm not bashing on FF or blindly singing the merits of Acrobat Pro, but AP9 is very fast and doesn't take up much RAM on my system. I wish there was an equivalent of OS X's Preview for Windows, it's actually one of my favorite components of the OS.