I'm doing this for our site right now. I have created a contacts application that stores whatever i want it to store on users. I am integrating this appliction into the regular login page, so we can get things such as the country they are signing in from on the general registration page - and then when they fill out other forms throughout the site it automatically presents them with the info they had previously entered... its actually pretty complex and taking longer then expected, but if you want me to email you an pre-alpha version of the software i'll likely be able to within a week or two.
This system may very well be overkill for your needs, so if you just want, for example, addresses and telephone numbers i recommend downloading telecom-number ref-itu and postal-address from CVS HEAD (aka OpenACS 5.0) and using those apps. My contacts app uses these tables to store data such as this for users, and they are made to store these extra types personal information.
If those packages don't cover all the things you want to collect i would also recommend creating a seperate table and not modifying users... unless you can use the general attribute storage mechanism - which may work for you. An example of something that uses that system are users "bios" if you want to look at the code. If you don't modify the core data model it will make upgrading to new releases of OpenACS much easier in the future.
