[Plugin: WP Super Cache] Very long page generation time

What could be causing something like this? The server loads are fine… 99% of the time everything works fine but very occasionally a page takes literally minutes to be generated…

<!– Dynamic page generated in 125.848 seconds. –>
<!– Cached page generated by WP-Super-Cache on 2011-03-10 09:19:09 –>
<!– Compression = gzip –>

Any insight would be appreciated — I just did enable preload mode, that might help but any other ideas?

john.