The other reason I have stuck with a 750GB internal hybrid drive is so that I can keep a 350-400GB subset of my larger iTunes library on the internal drive of my Macbook Pro, without replacing the optical drive with a second HD or having to use an external that can be more easily lost or stolen (like at meets).
I have just about every file I ever wrote or downloaded on my drive from the past 15 years, and with all those plus all my apps it takes up 250GB before I add my iTunes library. If I just add my favorite music with no videos or iPhone apps I'm up to 410GB. So, while I could live with a 512GB SSD, right now I have about 650GB used up on my hybrid HD. My main iTunes library barely fits on a 1.5TB external portable drive, but I only keep that as a backup.