Hey all,
My thoughts:
The small jump in processor speed is negligible (2.2 to 2.4). Almost not worth discussing over the long run.
The extra hard drive space IS significant, imho. In a MBP the hard drive is NOT a user serviceable item, and you will grow into whatever hard drive you have in your machine if you keep it long enough. Unless you enjoy being tied to an external drive for more than backup purposes, a bigger hard drive now prevents you down the road from either voiding the warranty to change it yourself, or paying a tech to do it for you.
The video card issue... 128 versus 256. This is an area where I feel people don't look deeply enough. People quote performance testing sites, such as barefeats, who state the the extra video ram only gets you "a few more fps", and at best just under a 10% performance improvement... which may or may not be related to the chipset and cpu, rather than the gpu.
Now, look at the games they used for their tests. Most of them came out years ago. Halo came out in 2003. UT 2004. Doom 3 came out in 2004, with a Mac version in 2005. Quake 4 came out in 2005, with a Mac version a year ago. Prey is a fairly recent release on the Mac.
So, my point is that they used games that are not current technology, and don't require 256mb of vram 99% of the time. This can be misleading when discussing whether 256mb or vram is better than 128mb of vram.
The gaming industry moves fast. 128mb of vram is fine for today. What about tomorrow? What about two years from now?
Not to mention that the OS is becoming more GPU dependent, as are many applications. Aperture is one, as mentioned above.
My thought process when purchasing a laptop is to always buy as much machine as you can, knowing you will have the machine for a few years, and that very few parts of it are upgradeable. If all you can afford is the 2.2 model.... it's a great computer! If you can afford the 2.4 model, you not only future proof your machine better, but it will have a higher resale value down the road also.
Good luck, and welcome to the Mac!