I'm writing this on my Mac Pro that feels like a new computer thanks to the SSD (solid state drive) memory that replaced my existing hard drive. A friend of mine used to talk about this idea ten years ago -- that someday RAM and flash memory would get so cheap you'd be able to fit an entire operating system on it, making it magnitudes faster than current computers. Thanks to the past decade of ever cheaper and larger memory sticks, cards, and RAM, we're finally at that moment. SSD drives are now available in sizes big enough for boot drives (including your operating system and space for apps), are available for many laptops & desktops, and start at just a couple hundred bucks.
Today I finished putting a 128Gb Crucial SSD drive in my newer Mac Pro. It was simple and the results are amazing. The hardest part was dealing with a new 128Gb SSD drive compared to my current main 1Tb hard drive. Thankfully I had a spare 1Tb drive to move all the music, movies, downloads, and document files to in order to get the operating system and application files down well below 128Gb in size. Next, I took my new SSD drive out of the package, opened my Mac, slid out hard drives, plugged the drive into a spare optical drive connector, and put it all back. Then I used SuperDuper to clone my now smaller main hard drive to the new drive, set it as the new boot drive, and rebooted. I followed the basic approach outlined in this tutorial (ignore the use of apps describe there) and was done, start to finish in less than 40 minutes (attaching the drive took 5 minutes, data copying took 33 minutes).
Overall, booting up takes about 1/3 as long. Applications launch in a second or two (even the bloated ones). Everything feels amazingly snappy, in the way that replacing a 5+ year old computer with a new one feels. About the only tip I'd give is that 64Gb is probably enough for most people if you can get iPhoto, iTunes, and all your large file storage to a separate drive. My SSD is barely using 25Gb for the entire OS, about 10Gb of applications, and assorted other files sitting on my desktop. I bought a larger drive just to be safe but I'm not sure it was necessary.
Currently, I'd put preparing your computer and installing SSD at the fairly technical nerd level but given that laptops with SSD pre-installed have been available for the past couple years it's only a matter of time before desktop computers start shipping with them. To any of my friends considering this, it's totally worth doing.
UPDATE: Jon Deal wrote me an amazing email last night detailing how to move the home directory to a new location using some command-line mojo and a hidden advanced user account feature I didn't know existed. He put it online last night here. It worked perfectly for me and saves a lot of headaches. I actually could have done this before I installed the SSD and before I shrank down the files/directories on my main drive to fit onto a SSD.