I used to lap rings, thinking that it can only help. That is kind of true. You do usually get more contact on the scope tube. The problem is if you remove the rings, and remount them (like if you swap scopes between rifles - which I often do) then the lapping will likely no longer be true, because the rings were lapped to the previous bases. Even if you replace the rings on the SAME bases, the rings will likely not take the exact same purchase on the bases. Not a huge deal, of course, as you can just re-lap the rings after mounting them back to the bases.
If I am mounting to two piece bases, I prefer to bed the rings to the scope tube, giving nearly perfect contact, even better than lapped rings.
Still, bedded picatinny rails and unlapped rings are my preferred method. Then I can switch scopes easily between any of my rifles, without worrying about anything.
Here is my base bedding video:
[video=youtube;Nv5KCXchSgY]http://www.youtube.com/watch?v=Nv5KCXchSgY&list=UU4cRVh7y8Rt6fTQCDfxJaFg&index=2&feature=plcp[/video]
I am not saying my method is better than anything else. It is just how I do it, and it works for me...