I have used a number of connected online tree sites: One World Tree; Rootsweb's World Connect, World Connect and the Allen County Public Library's wiki, WeRelate.
This weekend I entered in 5 generations of ancestors, or 62 names into WeRelate. There are tutorial videos and texts on the WeRelate site that I suggest you watch and read before you begin. I first created GEDCOMs from my Legacy Family Tree database, one for my father's ancestry and another for my mother's ancestry. I submitted them to We Relate and got back a log of possible errors. Most of them dealt with dates. Since the keyboard on my personal computer sometimes duplicates the number 1, I'll check for those mistakes. I then decided to just enter five generations by hand. Somehow my fathers parents don't seem to be connected to him even though I've gone over the steps of creating the individual and family entries several time. Once I get that straight, I'll blog about the process.
I was surprised that only 6 of 62 names were already in the WeRelate system.
I recommend that you check out the WeRelate site if finding out how you connect to others is of interest to you.