Even thought I use dozen of .com, net, org and so on, you don't have to wirry about link farm penalties. I'm doing this for at least 4 years now, hundreads of clients on wicked ( not to mention others clients from other places) and I NEVER seen a site penalized for my services.
Someone want to do some stupid things like to post the same article ever and ever only with different links: I simply refuse that order