very *large* gallery (4M+ pics)

[freeflight]

Hi,

I am thinking about using coppermine for  a very large gallery... which will be started from scratch but with existing users (who uploaded more than 4M pics into an other (much simpler) image hosting solution) - did anybody every do something like that? are there any limitations? I was thinking about gallery2 for the longest time but coppermine seams to be more mature (?)
to keep it simple I am going to limit it to only 1 album for each user (300k users so far) and we are also looking for a way to have users send pics directly from their cellphone (email gateway) - does anybody know about such an email gateway add on?
I am aware that we will have to hack a couple things into the existing system (spreading pics over several servers etc.)
How does for instance the "random" feature scale if there are 1M+ pics in the system?
feedback highly appreciated.