The geshi cache seems to cache "too much" (unnecessarily). See http://wiki.splitbrain.org/wiki:install:nanoweb?rev=1194490508
for example (as long as no-one clears the cache).
Independent from revisions and only dependent on its content, even the code of old revisions is cached. (Whereas the rest of the page of old revisions is not cached - and should not do so.)
That results in too much unnecessarily wasted disk space.