I\'ve been wondering what exactly are the principles of how the two properties work. I know the second one is universal and basically doesn\'t deal with time zones, but can
When you need a local time for the machine your application runs at (like CEST for Europe), use Now. If you want a universal time - UtcNow. It's just matter of your preferences - probably making a local website / standalone application you'd want to use the time user has - so affected by his/her timezone setting - DateTime.Now.
Just remember, for a website it's the timezone setting of the server. So if you're displaying the time for the user, either get his prefered timezone and shift the time (just save Utc time to database then, and modify it) or specify it's UTC. If you forget to do so, user can see something like: posted 3 minuses ago and then a time in the future near it :)