I got the base RIMac, but upgraded to 16 meg RAM through crucial. I had a budget and it didn't cover any other upgrades.
I use it for general computing but primarily with photography in mind.
At the moment I am still using my PC software, Paintshop pro X6 through Parallels. I don't know if you are familiar with PSP but it is more demanding on the hardware than Photoshop, especially using background eraser with large brush size, and once the layers build up.
Up to now Parallels on the RiMac has managed admirably, with no delay on using the brushes and tools, or with layers. It was a joy to use my Wacom pen on, the brushes being smooth and instant in application, no waiting for the computer to catch up which plagued me on the PC. I am using Nikon RAW files around 14 - 18 meg I think.
Fr my RAW converter I am still using Nikon NXD Capture ( the Mac version now though) , which is free for Nikon users and provides a useable RAW tool. It was slow on my PC and although much better in the RiMac still can be a little slow at times. Not a big problem mind, but it's not instant.
My intention is to use it until LR 6 arrives, apparently in March, which is going to accommodate the RiMac screen apparently.
Until then I am happy to use NXD.
The RiMac manages pictures great, in general use I notice no delays or lags and it is much much faster than my PC, which was an i3.
Would I have liked upgrades? Yes but I don't have an endless wallet for computer stuff. Are they absolutely necessary for my own use? No, not at all. Hope that helps.