The Blue Card requires that you have a job contract or very concrete job offer with a minimum salary, and will more or less be tied to that job: If you lose your job, they apparently can give you some time to find a new one, but you may get kicked out if you fail in that endeavor. Also, if you want to change jobs away from the one that originally got you the Blue Card, you'll have to get formal approval. (Edit: this would probably apply to a regular work permit, as well. I'm German, so I never had this problem. Still, you can apparently even apply to get a work permit as a freelancer, which would then make life much easier for you if you don't want to tie yourself to a Blue Card job for that long.)

Other than that, there seems to be no catch - the Blue Card is meant to attract highly skilled workers, so once that hurdle is cleared (>> minimum salary, university education, easier for certain high-in-demand sectors), the EU countries seem pretty happy to have Blue Card holders stay - as they should be.

Yep, the permit is tied to a specific job for the first two years[1]. From what I understand, it's pretty easy to get approval for a different job, as long as the job description is similar. Interestingly, my residence permit also says "selbständig Tätigkeit gestattet" (self-employment permitted), so it seems I could freelance here without needing a different visa.

[1] http://www.berlin.de/labo/auslaender/dienstleistungen/index....

So, still better than an H-1B :P

I think the blue card is only for some restricted occupations (in tech, science, mathematics, etc.) and has a minimum salary requirement (of about 46k euros/year). Which shouldn't be a problem for the HN demographic.

For IT occupations the limit is even lower: € 36.192 per year.

For workers under 29 years of age. 30 and above is something like € 52.000/year (at least for The Netherlands).