Hi Arno and welcome to ²ÝÁñÉçÇø!
As you already found out, the rules for immigration to PR are the same as in USA of which PR is a territory.
The chance that you would find an employer willing to sponsor you is really small, even if you have some special qualifications. The economy is in a bad shape and many people are without work. Even if an employer would be willing to hire you they would require that you have a work permit (or a visa that allows you to work).
To get a visa with assistance of a company you would have to work for them in Europe and try to get a transfer to PR.
Is it worth it, you ask. I'd say yes but of course it's a personal decision. I personally like it here and the chance that I go back to Europe is really small.
Finding a job is going to be difficult but if you have a financial buffer and/or your girlfriend has a good job you would have time on your hands and might get lucky.
You could also consider to start your own business, here or internet based (something you could already start over there..)
The easiest way to get your green card is to get married to your girlfriend and have her (or a family member) as your sponsor.