weird, i just experienced the same thing, on safari/mac.
the site is hosted locally on my mac whilst developing, and it has been working fine for a week. suddenly when i woke up this morning, admin pages took 30 secs to load until i disabled the cal plugin.
upon reenabling it, it slows to a crawl again.
so for now it’s disabled, but i really need this plugin.
any pointers on what to look for? latest version of both wp and ai1ec