The more, the better. The age old marketing ploy is not just a means to sell pricey systems. Win7 recommends 1gb, for good measure i would say 2gigs. The average flashy game wants say 1-2gigs, for good measure we give it 3. Thats 4-5gigs. Then pile on security software running in the background, any other background services from programs the average user installs lets say another gig for those, not to mention that many newer games come with additional software to "enhance" the gaming experience, game server clients, punkbuster, dlc centers etc. 6-8gigs is what you would expect in the average gaming machine.
Lets consider, a system more aimed at productivity, Office, Acrobat, browsing, email, 4gigs of memory would probably be more than sufficient, 2gigs for the OS, a gig for background services, and a gig for everything else. You won't max out that memory, but its better having extra you never use than being stuck with a machine thats locking up cause you don't have it.
More specifically to your question. When I purchased my laptop, memory wasn't my primary concern, that came down to going with an i7 or a Core 2 Quad, as in instances that were important to me, the mobile Core 2 beat out the mobile i7. It was a decision between the HP HDX1 and a Qosmio x505. The model I got was the top model(full HD, dual hdds, (ssd+hdd), number two nvidia mobile gfx card) and it came with 6gigs of RAM. Wasn't much of a consideration, as much as it was what was offered.
My media pc, only has 512Mb running Win7 Ultimate. All the unnecessary
services are disabled, but its more than apt for running HD movies even
without discrete gfx. But, basing my comment on the what the OP is looking for this machine to do, they will be better off with more than 4gigs, especially with it being within their budget.