The main reason I ever see this sort of thing is because my (modest, but not crazily slow) machine doesn't have enough memory—it only has 1GB, which definitely isn't enough for multiple tabs with typical bloated websites these days. If I've got gmail, youtube, and a few other tabs open, my machine will happily thrash it's little disk-drive out to accomodate them.... ><
[This is especially true if you're using chrome, which tends to use more memory per tab than other browsers because of its process-per-tab architecture (which is nice because of the isolation and controllability it gives, but it does make it more difficult to share memory between tabs).]
If I were in charge (I'm not because it's a work machine), the first thing I'd do is buy more memory.
I'm running an i5 w/ 6 Gig of RAM. I'm pretty obsessed with keeping my machine clean as well, so I'm not entirely sure if it is the slow machine, but idk really.
[This is especially true if you're using chrome, which tends to use more memory per tab than other browsers because of its process-per-tab architecture (which is nice because of the isolation and controllability it gives, but it does make it more difficult to share memory between tabs).]
If I were in charge (I'm not because it's a work machine), the first thing I'd do is buy more memory.