The first surprise was that after the pact (which was a simple click invite) I got a temporary power that gave me more endurance recovery and defense (Magic Lunchbox Girl is a kin defender). She got a corresponding temp power that gave her increased damage output and damage resistance. (The Eternal Newbie is a shield tanker, shield being the other feature on test heroside this time.) Unfortunately the power disappeared after some minutes. I don't know if you can get it over again by dissolving and renewing the pact. Perhaps I should test it, but not until I am finished with the other tests.
For the most part, it works as advertised. When Lunch was doing a sewer run (almost everyone had a tank or scrapper, so defender was highly sought after), Newbie showed off his energy shield at Atlas Plaza. He did not level up until some minutes after she did, perhaps because she was in another zone. Also note that only XP is shared. Influence is not, but you can do this manually later. Since you level up at half speed, you will get double influence. After she came out, the difference must have been corrected, because they dinged simultaneously while teaming in Kings Row. However, after she went on a bank mission and he not, she seems to have acquired a permanent lead. Or at least it has not corrected itself yet.The lead is moderate though.
We were automatically added to each other's friends list, but there does not seem to be any live status info like in a team. Generally, a minimalist approach, but it almost completely does what it sets out to. Another reason to play the best online RPG ever (with the possible exception of ZOMG! when it is complete).
[Edit: Logged on again and the xp is now equal again.]