Now that Adobe have finally fixed the memory usage issue with Lightroom 3, I get by okay with 8GB of RAM in a 2.5 year old iMac, processing full-size RAW files from a Canon 5d Mark II, and I routinely do fairly high-volume, fast-turnaround work and get by okay with this. I am normally working with Lightroom 3 and Photoshop CS5 open at the same time, and I am using both heavily. While I occasionally bump up against the RAM limit, it is really a faster processor (and maybe hard drive) that I think would be most useful to me, especially for faster exporting of large numbers of files. However, I am usually doing no more than a moderate amount of layering in Photoshop. Perhaps with heavy layering, things might bog down more, but that is really not something I would be doing for high-volume work.