My co-worker and I both just got new MBP's. She got a 2.2 i7, and I got the 2.5 i7. Both machines are just plain stupid fast, the only difference I see when using hers is the limitation of the 5400rpm drive on the base config. Mine has a SSD and I definitely notice the difference opening files and working with just about anything that accesses the disk.
Frankly the only reason(s) I got the 2.5 were because of Final Cut Pro X and Compressor. Not just for current workloads, but also for future. I like to get plenty of life out of my Macs, and I'd like the MBP to give me at least a good 5 years. I had considered getting just the base config and a Mac Mini to do the encodes, but instead I opted for the 2.5 and am very glad I did. After working on my first FCPx project in 1080/24 and seeing how even at times the monster 2.5 had some issues keeping up, it was an excellent choice for longevity. Added to that are large RAW workloads in Aperture or Photoshop, like today I needed to tear through edits on 180/3.2 GB worth of photos, it's really nice to have that excess processor overhead when you see it's pegged.
So with that in mind, I can only see the 2.4 or 2.5 being necessary if you do work that really is processor intense. Aside from that, the 2.2 is brilliant and will last you many years.