Hopefully it's obvious that you should treat your virtual workers well.
I was on a team of a few people that worked in one office and we worked virtually for another office. We weren't treated well and our moral suffered. We just didn't care about the work that much.
Once instance of getting crap from them was we would often lose connectivity to their office. The problem was on their end, but they took a week for them to fix it. Then we were asked, "Why are you a week behind?" When the same thing happened but to those that were physically in that office, it was fixed almost instantly.
With team moral low, they decided to have some team building. But they made us take a week out of our lives and go to them. Yeah, that didn't improve things.