lorax - 2:52 pm on Mar 18, 2012 (gmt 0)
I've seen this before but it's quite often one of the following:
1) calls to offsite resources (like Google Analytics)
2) bloated database (run repair or optimize on it)
3) un-optimized images (especially if run in a slideshow)
A client site had an issue similar to this and I checked all of the above to no avail. For several months I banged my head but couldn't find anything. The the next WP upgrade came out and it also upgraded the the database. Voila. What was taking 20+ seconds to load came down to 4. I'm still not sure what it was but we're happy it's better now.