I've just built a new Windows 7 desktop, maxed the memory to 32 GB finally replacing my 1GB memory XP desktop.
As i write this, there are 5 browser tabs open, notepad, one folder plus the ASUS motherboard AI Suite 3 software running in the background. No pre-built bloatware running in the background as there is no pre-built bloatware.
Task manager shows almost 3GB memory in use.
Shortly after mostly completing the build, I allowed Windows update to do it's thing, there were 159 updates to download and install. During this update, memory use went to almost 10GB!!
A machine with 8GB memory would have choked and slowed to a crawl during this process as the swap file/page file/virtual memory came into use.
Of course I have no idea if Windows update read my machine's memory configuration and adjusted itself accordingly, I suppose such a thing is possible. Since I'm avoiding Windows 8, I cannot speak to it's behavior at all.
Anyway, my point is to recommend a machine with the most memory possible. From my admittedly limited current experiences, I suggest 16GB as a minimum, 32GB if possible for maximum future headroom.
It does get expensive buying a laptop with so much memory, one of the reasons I chose to build a desktop instead.
If you can, steer away from any machine that still uses a spinning rust hard drive for anything but storage, aim for only SSDs inside the machine, relegate large capacity HDDs to external storage only. HDDS have always been somewhat fragile being susceptible to shock/impact damage while SSDs are essentially immune to such damage. A laptop with SSDs only will be far less susceptible to damage while on the move.
SSDs are way faster than HDDs for all computing tasks staring with loading the OS, loading programs, then loading files.
Yuppers, high performance computers can get pricey indeed, all part of GAS (Gear Acquisition Syndrome).