"Solid."

If memory serves, that was the catchphrase of Linc Hayes on Mod Squad as portrayed by Clarence Williams III.

Solid state drives--not the very latest or fastest technology, but still far faster than hard drives that must sometimes wait over a hundred microseconds for an actual physical hunk of matter to rotate around to the read/write head!--have gone below the dollar per gigabyte price point. (Remember how excited we all were when rotating platter hard drives broke that barrier?) Today, as I type, there's a deal at Tiger Direct offering a 120 GB SSD for $0.67/gigabyte before rebate, $0.50/gigabyte after rebate.

Under Linux, you can install on the SSD and then symlink from /home/myname/BigDirectory to a directory on your larger capacity old clunky rotating hard drive to keep all your collections of music, ISOs, images, and so forth from filling up the SSD while still having your various configurations and such on SSD for rapid access. (Windows finally got symbolic links for NTFS, so it should be possible to do something like that there, too.) Since you can bound the size of your Second Life cache, it should be possible to keep that there, too, which I hope would speed up your Second Life experience.

(Discussion here seems to show that it does, though people in that thread also point out that a RAM disk is even faster, and avoids wear on the SSD--as flash EEPROM, it has a limited number of writes on any given spot--but OTOH, the point of cache is to stick around until you clear it; you'd have to do something to back it up before you shut it down and move it to RAM disk before you fire up the SL client.)

Should you decide to go SSD, be sure your OS/driver and SSD support "TRIM", and tell your OS it doesn't have to play the usual games of scheduling I/O to minimize read/write head movement. Take a look at the Arch wiki or AB9IL's blog for suggestions for Linux.