Sitting here in one of my Uni's labs. 64 x Pentium D 3.20GHZ with 2GB RAM. And there are 6 such labs in this department. That's 384 of those machines which are on 24/7. Those machines could easily get an RAC of 500 and above, about 200,000 RAC in total.
If only I could put them on BOINC!
And that's just this department, there must be thousands of computers in total, if only... :(