CreativeMac has a nice little review of 24SevenOffice in an article where they present three "web 2.0" CRM solutions. I don't consider 24SevenOffice to be "web 2.0" (what is anyway?) though we do use some "web 2.0" features such as mash-ups, api's and hold your own data.
The application itself is slick and has quite a few features, even in the least expensive option. For instance, you can make recurring appointments, track products, and send e-mail promotions to all or some of your contacts. It's clear that one could spend a lot of time exploring the 24SevenOffice's capabilities, and continue to find new things you can accomplish; that's the sign of a good application.
Read the review at http://www.creativemac.com/articles/viewarticle.jsp?id=38582