yeah, eventually solid state drives (ssd) will completely replace mechanical hard disks, but since solid state storage is still pretty expensive per gigabyte, what most people (including me) do nowadays is buy a smallish ssd (mine is 120 gb) for operating system(s) and commonly used programs, but put their large data files (music, videos etc) on a larger, mechanical hd. if you are not a digital pack rat then 120 gb will probably be plenty and you won't even need a secondary hd.
ssds are FAST AS FUCK compared to old ass spinny drives. it's a very, very noticable difference. windows 7 boots in 5-10 seconds, most programs pop up in less than a second and so forth (photoshop cs6 now starts in pretty exactly 1 second on my computer, which isn't even very fancy)
so i fully recommend getting an ssd but check out the internet before buying. anything by the company OCZ is shitgarbage, do not buy their crap under any circumstances. they use bargain bin memory cells with worse quality than other manufacturers so some of their drives have 20-40% failure rates. there are other dogs too, so make sure you know what you buy
ok