This is the most mercenary discussion I've seen on Slashdot, ever.
If your employer isn't loyal to you (within reason) then you don't want to be there. Most of the organizations I have worked for - including some very big ones - actually do try to avoid laying people off in a downturn, at least skilled white-collar workers. In a knowledge industry if you burn your workers every knows and it gets tougher to hire in the future.
You already know whats right for you - the other job. That means you need to leave - but doesn't mean leaving the current company (& coworkers!) in the lurch. Ask the new employer if they will give you a couple of months before you start; if so, get an offer letter with those terms. Seriously - I just hired a programmer and a project manager on these terms (2 months and 3 months respectively). They needed the time to close out projects, train new hires etc. I was impressed that they were loyal to their old employer - and presume they will leave me one day with the same grace and style. Their old employers (who couldn't match my offer) were pleased that they were willing to stay that long, and will in the future give them glowing recommendations - and might hire them back. Co-workers don't feel shafted etc. Did I want them sooner? Of course - but they were the right people and I'm willing to wait.
Now, your current employer might tell you to stuff it, and to clear out your desk. Or that they will hire someone and they only want 2 weeks and then your out. Fine - you have been loyal and done your part, and the new employer presumably will take you sooner.
Loyalty means doing your best in a hard situation, not picking between 2 weeks notice and staying forever.