what's with all the portfolio sites?

When I first started trying to promote my services, I signed up with Portfolios.com. It's a well-known portfolio site which is part of the Create Network - hence, where Create Magazine comes from. While I've gotten a few inquiries and a few jobs from posting my portfolio on this site, I've also received a wonderful invitation to join an Advisory Board for an up and coming design software. Very cool.

The crazy thing is, I signed up for that gig last February and never heard of these portfolio portals before. Now, they're everywhere! I receive generic messages about once or twice a month saying, "Hey, I saw your portfolio and think you'd be a good fit for our online portfolio tool. If you're interested, visit www..." I found CarbonMade.com recently this way and signed up because the site looked pretty cool and it was free. But what about all the other ones in between?

What is it about this particular portfolio sharing system that makes their creators think we need more and more of them? Are there really that many people out there using the sites? Furthermore, is anyone really benefitting from them all that much? In other words, are designers really generating a solid clientele this way?

The thing that worries me a little is that the work is unprotected. Being that my subscriptions to both of these sites are about to run out, I'll deal with it in the mean time. But, isn't there a pretty good chance that someone can just right click, download your portfolio swatch and go from there? Am I being paranoid?