Aperture 3 from iPhoto

I drink the Cool Aid and use almost everything new Apple throws out there. I liked iPhoto, so with Aperture 3 being pitched by Apple as an upgrade to iPhoto users and not so much as a professional tool I went for it. I'm not a professional photographer, but really appreciate the touching up tools in Aperture. I followed the migration steps on Apple's website, now I have a Aperture library that's something like 25% bigger than the iPhoto library (that's a lot of gigs). Why is this? These instructions seem really vague: (Apple - Aperture - How to move from iPhoto to Aperture.), particularly step 5. What happens when I merge my masters? I did, and it told me the step was irreversible, now I'm concerned I've permanently compromised my iPhoto library and I'm locked into Aperture, which I'm nervous about because of the seemingly much larger library size, and that the application seems to run much slower and hang up more often. So now I'm supposed to delete the iPhoto library... that's it? Any other supporting files? Should I delete iPhoto since it's pretty now empty? Any input on migrating from iPhoto and the repercussions is appreciated. BTW, running Snow Leopard 10.6.2 on a 2.5 Core 2 Duo Macbook Pro.