i have one really big folder full of everything. i browse it with adobe bridge or quicklook. recently i've been tagging every picture i add by putting keywords into the spotlight comments field.

Anybody know the storage limit of iPhoto on a new Mac ?

afaik it can be as big as your hard drive. if you had 10 000 images or something it might start to bog down a bit.

Thanks. I guess it would depend on what else was on the hard drive, and how big the images are ?

Another question: an external hard drive would be a good place to back up images, as well as an potential overflow capacity ?

you probably want an external hard drive at least as big as your internal drive so you can keep proper backups. (in fact you definitely want this - how much is your data worth to you?). If you're using Leopard, it has automatic backups built-in. Just plug in an external drive and turn Time Machine on.

Aperture allows for custom tags

How is the new iPhoto on Leopard? I looked at it in the store and it sorts images by "events" instead of by film rolls. Seems kind of odd.