Object Cache Slowing Down Site?

After trying out a series of caching plugins for my WP 3.0 multisite installation, I still can’t figure out why my site’s performance is so atrocious (~8 seconds).

I’ve tried disabling and enabling my plugins, no success so far. I am on shared hosting, so I had attributed it to that, but I now think that it seems to have some connection to the Object Cache.

I looked at the queries and the MySQL lookups are executing in .16 seconds, the rest of the time is PHP server processing (or so it seems).

I inspected my object cache with the Debug Objects plugin – it’s showing a huge lists of objects in the cache, 600, even though I have flushed it. Also, none of these items in the object cache seem to be helping the site to load any faster – I can’t get rid of them though.

Any thoughts/ideas on how to get my site running quickly again?

Thanks!
Jordan