I might, just might have a clue to this.
I mainly use Opera as my web browser, on account of it being much better and faster than IE6, and one of the things it does is to tell you in the bottom right hand corner exactly what it is doing.
I do not get the problems that you guys have mentioned either at home or in the office (both have Broadband) but I do get it on GPRS, which is a packet switched network which uses spare capacity on mobile cells. Because GPRS only takes spare capacity it is relatively cheap, but it is subject to the vagaries of availability, so sometimes is much faster than others.
So, putting the last two paragraphs together, I do find that things freeze on GPRS, and I can see exactly what it is doing, and every time it freezes it is interrogating oz.valueclick.com.
So it may well be the fecking ads, guys!
W