Overworked and cheap labor
I think the discrepancy between unemployment and job openings is due to salary. Let's face it, a lot of IT jobs pay OK but not great.
A large number of network admins and desktop support people come from 'PC savvy' people that migrate over to the field, not someone with formal training.
Cheaper.
You can be a a manger at Arby's and paid better than a director of IT support.
So sure, there's openings - those qualified people don't get hired because they'd have to take a hefty pay cut.
The overseas people? Cheaper.
Overtime in this field has always been a massive issue - even allowed by law in many cases. No one complains now because "you should be happy to have a job".
Net result: Pay for 3 people, get the work of 4-5.
Cheaper.
So what happens when something falls apart?
Highly paid consultants.
Is it really cheaper than good, competant staff with a well rounded background, capable of quicly acquiring new technologies?
Debateable.
== John ==