Practically, SSDs are things that behave like hard drives but have microscopic access times in addition to their ludicrous-speed serial transfer rates. As a result, anything that loads from an SSD, like your OS, will load much faster.
For that reason, it's traditional to install your OS and apps on the SSD, and things that don't need blazingly fast access on the HDD. If you are listening to MP3s, or downloading from the web, your data rates are low enough for any HDD to handle it just fine.
Want your machine to boot faster, load faster, and seem more responsive to your input? Install on an SSD. Just be sure to read some of the articles on the care and feeding of an SSD so that you know what controller mode to set, how many drives should be attached to your system when you install Win7, and the flying speed of an unladen swallow.
Two points for identifying all of the movie references.
What WyomingKnott said. Personally if you aren't bothered by wait times, then a SSD is an extra expense. Personally I'm not bothered by wait times. I'm not that impatient. On the other hand, I know if I were ever to get a SSD, I'd probably have a hard time going back to a standard HD.
sadly load times DO matter alot to me because i get sick of being stuck in a loading screen for 5 mins or less to play a game online, OR just play singleplayer load times are bad, 360 worse. xD
and im starting to get into ending the drawing i make. (more like paint them on the comp) and it takes easily 10 mins e to load a pic.. (laptop and i3 (is better then what i had last) and a 7000 RPM HD it sucks..
I just upgraded to a SSD in my main PC and it makes a big difference on some things, but not on others. Windows boots faster, my games load faster (but some in-game loading is the same speed or not a noticeable difference). While it is really nice, it is still really expensive. If I could buy a 90GB SSD (second gen sandforce with async nand) for $50, I would install one in every PC I own.
I really want one for my HTPC, but until prices drop it'll have to wait.