I work in Facilities Management... so, while I don't actually do design, I work with Mechanical (HVAC/R), Electrical, Plumbing and Fire Protection systems.
I use Map3D currently, but, have been looking at ABS and Revit System. RSys is a relatively new product, I only know like one guy in the city using it so far... so, I know it's got a little ways to go to reach maturity. I believe I've read that ABS is selling like hotcakes right now. It's good to see MEP designers catching on to BIM/intelligent drafting and design. This is a good step forward (so, I'm sure the FMDesktop team is taking note of all of this and working on working with MEP data from ABS/RSys to make us Facility Managers happy... ~fingers crossed~ ;) )
I just thought I'd point you over to the Lazy Drafter... no, that's not an insult, that's what he calls himself. Todd Shackelford talks about your current options, and the things that Revit Systems has going for it, some potential headaches, and the bottom line. Enjoy.
(does anyone know of any other MEP bloggers out there? they seem to be a rarity, I'd love some links if you have them, here's another, Kelly Swa, the Redneck CAD tech Bucking the System)
Oh! And something handy to keep in mind... this blogger talks about the proper way to dispose of / recycle your electronics; such as computers and cell phones.