For the last while both my laptop and desktop have become sluggish, especially when it comes to batch-processing high volumes of large RAW files. I've been holding out on upgrading my main computer to a new iMac or Mac Pro, depending on what apple release in the next year. After seeing the specs for the new 27" iMac, that's likely to be the way I'll go.
With no plan to retire the macbook pro, I decided to replace its hard drive with a solid state hard drive (SSD). I expected the performance increase to be significant, but my expectations have been far exceeded. Boot-up time has gone from 4 minutes down to 30 seconds, and normally slow-to-start applications such as Lightroom seem to open instantly. The drive I got is an OWC unit from macsales.com, and it worked out costing about $1 per gigabyte. The drive I was initially sent turned out to be faulty, so I had to pay for a shipping return to the US (as expected), but the customer service was excellent and the replacement drive arrived within a week. No problems since.
Installing the drive was pretty straightforward using step-by-step instructions from iFixit.com. I can't recommend this solution enough if you want a relatively cheap performance increase to your current setup.
More coming soon...