Hey all,
I seem to be constantly replacing wheel bearings.
The rears were last done about 2 years ago (30,000km) but it seems they are now squeaking again.
 
What is the expected life of a set of wheel bearings for the SW20s? (specifics: Turbo, LSD, ABS)

Depends on a number of things, but 30K is very suspect.  Are you using Toyota Genuine, or a similar quality bearing?  How often do you tow your boat trailer into the tide and submerge the rear wheels?  (Only joking on this one)  Very rough, gravel roads, perhaps?
 
Were they fitted correctly last time?

One thing that comes to mind is 'South Rd' in Adelaide. Notoriously bad with manholes, potholes, inconsistent tarmac and all sorts of other problems for a 'main road'. I've also discovered my front Tein SS struts are leaking. So if rough roads can have an effect on wheel bearings too, then it seems there is some commonality there.
 
It is possible they weren't done properly, as I had brand new inner hubs to go in with them.