Seems like plenty to me for a laptop, do you bump up against that limit for what you do on a laptop? (I'm curious.)

He might need virtualization, which is essential for any web dev who wants to target the mainstream. You might have multiple VMs up so you can test different versions of IE (no IE 6 on Windows Vista or 7). When you add in Photoshop, Firefox with Firebug, and Apache, you really start pushing the limits of 4 GB.

I suppose it depends on what exactly you're doing with the virtualization, but if it's just IE testing, I've found 4GB to be plenty -- performance is fine with small amounts of memory in the virtual machines, which I assume is because their usage of virtual disk-based memory is quite fast due to the SSD.

Can't speak for the GP, but I frequently work with multiple Windows VMs (think large Oracle and SQL Server databases), and 4GB starts to feel a bit small.

My ideal machine would have more than 4GB RAM. It could even come at the expense of a smaller internal storage, because I'd use an external Thunderbolt drive to store client stuff.

So I might be sticking with the MBP for that reason..

I use Windows, but just yesterday I noticed I was using 5.47GB and I didn't even have any VMs opened. Just VS with Silverlight, sql server management, couple of browsers with the silverlight plugin opened.. 6GB of RAM payed of I guess

All good OS's try to use all the RAM availible (within certain limits of course). My RAM is almost always at 80% usage and above even with just a couple of lightweight applications running.

I was talking about "Commit charge" which is the memory actually used by the processes. You can see it by enabling the Commit size column in task manager. Which doesn't even include all the memory process actually uses. Check this for details on Windows if you're interested http://blogs.technet.com/b/markrussinovich/archive/2008/11/1...

As suggested, I use VMs fairly often, but just Firefox + Aptana + random other stuff can bump into 4GB on occasion. I could probably make do with 4GB, but I'm hoping the next iteration will go to 8.