Well the good news is Autodesk is making plumbing the focus in Revit 2012. The bad news, however, is we're stuck with a thrown-together implementation for another year.
We've found that there are just not enough plumbing systems in Revit. Because of this, you can't assign specific pipe types to Vent, Storm Sewer, etc. The elbows and connectors typically have problems connecting also.
Things to take note that may help:
-Avoid trying to system up your plumbing fixtures/piping. (Until this is fixed and works better, just avoid it at all costs. You'll spend more time trying to get it to work then it's worth messing with)
-Run your horizontal pipe in plan view and your vertical pipe in your 3D riser.
-Make sure you set your view style to "hidden line" when printing otherwise all of your pipe will blend together.
-You can use "key schedules" to fake connection/fixture data until you have a better understanding of how to get FU's and GPM to flow through the piping (which still works when it wants to it seems).
-Use filters based off worksets (as opposed to systems, since there just aren't enough plumbing systems in revit) so you can more easily visualize what is going on. You can also use filters to make certain lines have different line styles and weights.
-If you need to slope your pipe, do it early on in the mains. The branches and individual fixtures will automatically slope as necessary to connect to the main. If you try and slope after all the fixtures/piping is placed, you'll have nothing but problems.
We have been able to get our drawings to look very similiar to CAD. If I think of anything else, I'll try and add it to the post.