We all know that it's really important for an impatient SaaS user to not make them spend too much time filling forms. Having said that there maybe some important fields that needs to be gathered during the registration process for future reporting purposes.
Currently, the registration form I have only asks for:
Should I be collecting info such as:
I would say you should at least get First name or Nick name to make your communication to the user more personable. You can always collect the rest in stages, when customer will want something from you like free calculation or PDF doc or what ever.
Also now day I would suggest integrating facebook connect. It doesn't get any lazier for the user than that and you can get all the personal info they have in facebook.
Every additional piece of information you ask for will reduce the sign up rate.
Therefore you really need to ask yourself how valuable each piece of information is to you.
Note that facebook connect apparently requires the user to authorize which information should be passed to your website. So it is useful as an authentication mechanism but unless people have a reason to tell you the name of their favorite pet and music group, don't ask.