A good discussion arose on this question a while back - it might be worth checking out http://news.ycombinator.com/item?id=1714184 and the original article that spawned the discussion -> http://weblog.muledesign.com/2010/06/unsuck_it_special_byeby...

I tend to prefer using the 2nd person, if I have to choose one over the other.

[edit] - Sorry, should also add the link to the Yahoo patterns article, which also recommends the 2nd person http://developer.yahoo.com/ypatterns/social/core/yourvmy.htm....