Does the MXD Defrag program still exist in ArcGIS 10? Additionally, what settings/options have you identified to help keep ArcGIS 10 running fast?
The MXD Defrag program is installed (on my Win 7 machine) here:
C:\Program Files (x86)\ArcGIS\Desktop10.0\Tools\DocDefragmenter.exe
Just a couple of things I've changed so far - In the Advanced setting utility:
I set the temporary metafile size limit to 10MB. Not because of anything I've run into in Arc10 yet, but I did have problems in 9.3 and earlier, and this setting seemed to help.
I set the Output raster buffer size to 32MB in order to improve image export speed.