Go to your profile and copy and paste the link that is in your browser address bar. This is your profile link.
Your link for instance is https://www.odesk.com/o/profiles/users/_~019d3b36b5e19e1c19/
Unfortunately Luvisa, as Suzanne pointed out, there is no nice clean permalink. Using that lengthy URL on a card is not going to work well! This is definitely something oDesk should address, but hasn't.
You could use something like tiny url to shorten it, but then you'll loose the oDesk part. Grr. Digitally, no one cares how long or akward the link is, but it's a pain-in-the-butt in print!
What I've done is set up my own website and then used some of my best reviews from oDesk on that site. I ask all the clients before I do this and no one has ever said no. They've even allowed me to use their book covers on my site.
The website gives me the added bonus of being able to use it for clients that don't come through oDesk as well.
Once I get around to making business cards, I will use the address for my own website.