The problem with lazy registration is that not enough people are familiar with it, so they will probably get confused.
Case in point, I built http://www.taxbonus.gr/ (sorry, it's in Greek) a few weeks ago, it only requires registration if you want to save your session. It doesn't have enough people to tell, yet, but my biggest fear is whether or not people will be able to tell they're logged in.
There are plenty of visual cues (such as asking you to sign in if you enter data while signed out), but you know how confused some people get, especially if they're expecting something else.
Case in point, I built http://www.taxbonus.gr/ (sorry, it's in Greek) a few weeks ago, it only requires registration if you want to save your session. It doesn't have enough people to tell, yet, but my biggest fear is whether or not people will be able to tell they're logged in.
There are plenty of visual cues (such as asking you to sign in if you enter data while signed out), but you know how confused some people get, especially if they're expecting something else.
I'll let you know how it goes, though.