I'm using Cimy's plugin to add extra pertinent fields that are also categorized for private profiles via 'WP User Frontend' plugin and a mix of my own development features and extra plugins. I've used other types of plugins that offer similar features (like 'S2Member'), but this one seems to have the basics down pat with database organization, structure and simplicity ('S2' is excellent in its own right and I use it frequently, but it's a little too cumbersome for many of the simpler projects out there). If you're looking for an excellent database solution that allows you to easily create new profile fields and categorize them while also allowing you to customize the individual profile fields through the database via PHPMyAdmin, etc. (which is just the start), then 'Cimy user Extra Fields' is an excellent solution (and works well with other plugins too)! - Good job man!