Based on the recommendation of one of our engineers (thanks Nick!) I'm trying out this Seagate hybrid Solid State + 7200 RPM drive ($175 at Amazon: Seagate Momentus XT 750 GB 7200RPM SATA 6Gb/s 32 MB Cache 2.5 Inch Solid State Hybrid Drive ST750LX003).

What makes it a great efficiency hack?  The idea is that I'll get the benefits of blazing fast boot up & application opening speeds, combined with the 750 GB capacity of a traditional drive.  Here's a description of the drive from the manufacturer:

Boot-Up Time: Momentus XT drives are known for incredibly fast boot-up times, and now they are even better with FAST Factor boot technology. This system boot-up technique can reduce your boot time to mere seconds for a fast cold-boot start. It can cut your system start-up time by up to 65% over a traditional HDD. FAST Factor boot technology will deliver the fastest boot possible, whether you boot your system once a day or once a week. Your OS boot-up files are always there, ready to work.

Flash Management: Momentus XT solid state hybrid drives also implement a management feature that provides seamless integration between hardware, firmware and high-speed NAND flash while maintaining data integrity under all conditions--any system, any OS and with any driver.

Adaptive Memory Technology: Adaptive Memory technology delivers SSD-like response from the applications and files you use the most. It lets the Momentus XT drive selectively tackle frequently used data, copy it to the flash, track its relevancy and keep the flash current. You get the instant response experience you need to perform at your best.

I haven't tried it yet, but I've ordered it.  I'll let you know what kind of performance improvement I see.  The reviews are very positive, and I'll ask Nick to post his experiences here.  If you've tried this drive and have any feedback on its performance, I'd love to hear about it.