The ongoing meltdown in the financial world is leading to a massive layoffs in the investment banking world, which are widely expected to spread to the economy generally. This will result in a make or break test of the value of business / career oriented social networking sites like Linked In and Xing.
If they really do help people find their next role faster, they will become a key way large numbers of people manage their careers (with consequences for search firms and HR recruitment teams in large corporations). Even more so if they are instrumental in people finding roles that better suit their talents and interests than the ones they've been tossed out of. At the extreme, this could be the time when there is a permanent shift in the mainstream mindset, and most employment relationships take on a significantly stronger "freelance" flavour. (Ah, don't you just love that phrase "at the extreme"? As if we have any sense of what that really means any more.)
On the other hand, if they fail to deliver value, with many users finding them a waste of time (if looking) or a major distraction (if one of the lucky still-employed), then the sites are likely to face any or all of the following: slowing membership growth, abandonment of profiles (which happens today more than is generally acknowledged), and - again, at the extreme - public vilification and negative user reaction to ads.
Personally, I hope they do work. So, if you're looking and I'm on your network, feel free to contact me.