NHibernate, DateTime and UTC

We are in the midst of doing a total rewrite of our Software, and one of the things that has come up is date and time. How do we do it, how do we store it, and how do we ensure that we can compare DateTime from one timezone to DateTime in another timezone. After a lot of research, we settled on using UTC (or UCT depending on your preference). FxCop will take care of ensuring we use UTC (for the most part), or so we thought...