Not too long ago a 120gb SSD and 4gb of memory made for a great windows 7 platform.
Now it seems you need at least a 240gb SSD and 8gb of memory to run well & not be worried about running out of space.
Given how things are going, I'm starting to lean towards 480gb SSD and 16gb of memory when possible just to be on the safe side, especially if you want office & room for game installs left over.
An interesting thing is to watch the memory usage monitor when installing the 1 Gig + batch of updates for Windows 7 SP 1 fresh installs and see how much memory it feels free to gobble up.
Then of course there is the whole thing that the 1GB + of initial patches for a windows 7 install takes about 10x longer than the actual initial install of the OS, no matter how fast your SSD and CPU are, or how much memory you have it seems.