I use I RIP and am happy I do, but- the issue no one has really mentioned here is that unless you are using ImagePrint, you will be plunged into the world of CMYK profiling. First of all, this will require a more expensive piece of software than most prosumers generally use like the EyeOne packages or ColorVision.
Secondly, it will require a major learning commitment to issues like dot sizes, light ink limiting or not, individual ink limiting verses total ink limiting, GCR, channel linearizations, dithers, etc..
I assure you, it's not for the faint of heart. It could well be weeks, and lots of paper and ink, before your first print.
Tyler