Slow sites with multiple subscriptions?

Hi,

Come across a strange problem recently and wondered if anyone could advise or had come across this before. We've got a large MS install with 7000+ sites (student blogs).

One tutor in particular was subscribed to 1000+ sites. (all student blogs from one faculty).

She found that ANY wordpress site, front or backend took over 5 seconds to load.
This was regardless of theme, content, plugins. Even a blank site with 2010 theme and no plugins took 5 seconds to load.

Other users (myself included) the site loaded immediately, the only difference being the number of total sites she has subscribed to.

What is going on in the background to slow things down for her? Is there a wordpress background task that is fired every page that queries each and every one of those blogs perhaps?

I doubt I'll get an answer, just wondering if anyone had come across a similar problem.

Alex