At QGIS startup I get the message: "QGIS couldn't find your GRASS installation. Would you like to specify path (GISBASE) to your GRASS installation?" (Windows 7) No amount of rooting around the directory structure in the GRASS directories solves it. Tried uninstalling/reinstalling, no joy, but I also noticed that my plugins were still there, so the uninstall does not appear to have been fully clean.
I have a perfectly working installation on another Windows 7 machine that I installed just last week, so no clue why there's a problem on this machine.