Thanks chas_m and bobtomay for answering so fast!!

it's absolutely clear for me now how iPhoto works, and at least for me is wonderful, it's a great way to manage your photos in a so easy way [just yesterday I discovered that if you edit the artist name in iTunes from i.e. TOOL to Tool, it changes the folder name too awesome!!]

Having a backup of my photos is like having a backup of your music, no? I mean, of course is easier to re-download a Pink floyd album than all of your photos... but making this comparison made me realize that you always say "make a copy" no because iPhoto library is unstable or easy-to-corrupt, its just a safety measurement.... for me is like "your music has never stopped working, neither your photos, but if something goes wrong is easier to download an album that a lot of people in the world has, than a photo album that only you had".

I don't know if this is unusual, but I couldn't get used to Aperture :S I don't know why, but it wasn't "comfortable" to me... but iPhoto, oh man, is terrific!!