You need to earn 2000 points for the
rel="nofollow" restriction for your website link to be lifted.
Note that links in your "About me" section will always have the
rel="nofollow" restriction applied except for the link in your
Website field. It has to be an exact match though, if one has a trailing slash and the other doesn't then the restriction is applied anyway.
To rephrase that: If you enter a link in your
Website profile field, and use that exact same link in your About Me section, then that link is not given the
Jon Skeet lists
http://csharpindepth.com/ as his
Website link, so the exact same link in the About Me section is not given the
nofollow restriction. All other links in that section do.
The limitation is per site; if you have multiple, associated accounts across the Stack Exchange network, the restriction is not lifted for accounts with less than 2k even if other accounts have reached 2k already. Jon Skeet's Code Review account is well below 2k and has the
nofollow restriction applied to his links.