We have been in the process of evaluating Revit structure for several years now. until the 2008 version came out, my company felt it was not ready for "prime time". We have now been using Revit 2008 for about the last 6 months, by a small group highly trained specialists.
Our experience is very mixed. some things are nice, but some things are so very frustrating. Sheets of general notes are one of the most frustrating, as the text editing capabilities are very sub-par. I do like having a 3D model to play with, especially when the architect sends his revit model. Then I can cut sections wherever i want them, regardless if he has his sections cut yet.
Generating the model is very fast and works well most of the time. Some geometry is a problem, as stated above. Generating the actual production drawings is still very tedious at times, given the poor 2D drafting capabilities.
As for hardware, here are a few recommendations. A fast processor and fast RAM are important. Revit does not support multi-core processors, so consider this in choosing. A faster dual core may be better than getting quad-core here. Get as much RAM as you can. 4GB with Windows XP is recommended (well 3GB, but usually 4 is easier to install in matched pairs). Revit does not support 64 bit operation yet, so you don't need a 64 bit system. Get the fastest RAM you can get.
Revit is not a big hard drive user, except when opening/saving files. But I would still get a large fast hard drive. Running over a LAN to a central server will slow down your save/open speeds. So if you use a server, learn about work sharing and central files.
Revit also does not require a super high end graphics card. Revit runs much quicker on my machine than Autocad Architecture does with similarly complex 3D models. I would look for a mid-range workstation card with 512MB ram. I have an nVidia QuadroFX 1400 and it runs just fine, even with large 30 story models. The exception to this would be if you want to use the new rendering engine in Revit 2009. Then the faster graphics card the better, as the renderings, even simple ones, can take many hours.
Revit does not support dual monitors, so I would recommend one large monitor, say 24" in size or better.
Obviously, all of the things I listed above that Revit does not take advantage of, other applications you use may. So consider those when buying. Here is my workstation specs, and it runs beautifully with Revit 2008 and 2009. Granted this was top of the line about 2 years ago.
Dell Precision 380
Pentium Extreme duo at 3.46 GHz
Windows XP Pro
4GB RAM
quadroFX 1400 graphics
75GB 10000 RPM SATA hard drive (runs about 1/2 full right now with Autocad ADT 2004, 2006, 2008, Revit 2008 & 2009, Staad, Etabs, ADAPT, Enercalc, mat3D, Mathcad, PCA, etc. installed)
Dell 20" LCD (24" on my wish list)
Hope this helps some.