One of the Vista innovations that caught my attention early on was ReadyBoost. It lets you take a USB 2.0 flashdrive as virtual memory to enhance performance. Note that this does not add to system RAM. So, you won't see your available memory go from 1GB to 2GB if you add a 1GB flashdrive.
I stuck a 1GB Sandisk Cruzer Mini USB 2.0 flashdrive in my cheap PC. Since Vista was using 128MB of my 1GB system RAM for shared video, I had about 860MB of system RAM left. Vista assigned 870MB of the USB drive as ReadyBoost virtual memory. It reported that the drive was capable of 5789 KB/sec for random reads and 3573 KB/sec for sequential reads. Vista's minimum requirements are 2500 KB/sec and 1750 KB/sec. So, my aged flash drive more than met those specs.
I ran what seemed to me to be one of the most memory intensive apps I use, Virtual PC 2007 Release Candidate (running a Linux Guest OS). I didn't take any hard numbers. But, the system overall seemed more responsive than it did without ReadyBoost.
You can read an interesting Q&A with Matt Ayers (Microsoft Windows Client Peformance Program Manager) on Tom Archer's blog at...
...to get some real details about this Vista feature.