The user.cssprefs module is built over 60 times per minute globally. This isn't too surprising since it's embedded in the page and can vary by user. So this will likely reflect page view traffic of logged-in users, as well as cache population for logged-out users.
However the user.options and user.tokens module are both generated only 11 times per minute.
Figure out why this is happening and/or bring it down.
EDIT: It looks like this module is redundant. It should be merged into the user module as additional stylesheet. However we can't do that until we change the module to output nothing for logged-out users (e.g. any default styles should become part of a core or skin module). This because "user.prefs" is embedded while "user" is a separate request and we don't want to add a separate request for all reader views for this one line of css.