NullifyNetwork

This is an excellent usability study comparing the major webmail providers sign-up forms out there, it almost certainly has an applicability to all software development to a degree:-

http://www.cxpartners.co.uk/thoughts/web_forms_design_guidelines_an_eyetracking_study.htm 

So take a look.

It covers things like making name fields appear as one entry so they require less thought to enter, and making mobile phone fields not take an age to decide what bit goes in which box.  There were also some good basic layout hints and talk of when to use groupings and when not to!