I have just got a MacBook Pro and have been using it (+Fusion) to develop on for about a month now. The purpose of this question is similar to Hidden Features of C#; to become
Just extending this out slightly from the original question, there are some of us doing Delphi Windows development work on virtual machines, too.
I've got a MacBook Pro (1st gen) with a couple of gigs of ram, and a recent iMac (with 4 gigs of ram). I've had more luck than xanadont with external drives, running a couple of different brands on Firewire 400 and finding them to be fine with 16-20Gb VMs. If I'm going to be in one place for a few days (either in the office on the iMac or on the road with the MBP) then I'll copy the VM to the local drive but as a rule it's worked fine for about 2 years now.
I started with Parallels, but there came a point when they started releasing versions that hadn't been regression tested, and sometimes basic stuff would suddenly be broken in the current release. Simple fix, stop downloading the new version and stay 3-6 months behind everyone else. Then I needed to give a VM to a colleague and had to go through a few hoops getting it out of Parallels and into VMware. At that point I tried the Fusion beta, had first-hand experience of moving a VM between Mac and Windows (with no real fuss at all) and that persuaded me to switch to Fusion. I have to say, Fusion is an excellent, stable, reliable tool.
I run WInXP Pro SP 3, Delphi 7, Delphi 2007, SQL Express and various development tools on my VMs (I tend to have a VM for each of my clients).
And I agree with xanadont about the 1Gig ram thing - mine tend to have a gig and no more - I didn't see any real change in behaviour/performance with >1Gb in the vm, so it's better off given to the host operating system rather than the virtual one.
This is not purely .NET related but it is in the vein of the using Spaces item in the question.
Trackpad tips for a MacBook running Leopard (may not be supported in earlier OS X versions):
Set System Preferences, Keyboard & Mouse, Trackpad to use Two Finger Secondary Click. This allows you to use two finger taps instead of the Control + Click combo for the Secondary Click (better know as the context menu to us .NET developers).
Set System Preferences, Keyboard & Mouse, Trackpad to use Two Finger Screen Zoom for magnifying an area in the screen by holding the Control key and scrolling up or down. This is useful for quickly magnifying small fonts or image detail in any Mac application and in Windows running under VMware Fusion. You can pick either the Control, Option or Command keys for zooming by clicking the Options button along with other settings.
I use a Mac Book Pro as well but I run Vista. I set aside a little space so I could also run Leopard and just use Boot Camp. You can use Boot Camp to just boot from windows so you never have to deal with Leopard unless you want to.
I would highly reccomend it because Apple makes great hardware while Microsoft makes great tools (and also great OSs, I love Vista)
go ahead and downmod me for being a fangirl, but I've found what works for me.