The user profile system is completely customizable so you can easily add Skype and Jabber to your site if those properties are of interest to you. You only have to declare them correctly in mojoProfile.config. See the documentation here:
Custom profile properties come from the mp_UserProperties table and are stored as text data in key value pairs. Some properties were already existing before I created the custom profile feature so these properties are mapped by name to existing columns in mp_Users.
I'm not really interested at this time in optimizing the data types for existing fields in mp_Users for several reasons.
1. I have limited time and there are much more fruitful things to work on
2. The benefit of these optimizations would be so small that they would be hard to measure. Furthermore they are already more optimized than the custom properties in mp_UserProperties. We are already favoring flexibility over optimization here.
3. There is potential to introduce bugs by fixing things that are not broken