How long before we need externals?

With game installs ranging from between 20-40Gb's how long before we start to need external drives and are Microsoft going to make us buy official?
My 360 game collection was at one point over 120 strong, if ever i fancied a quick couple of laps on one of the racers, pop the disk in and away you go.
With having to install games and it taking so long, I can't see old games getting a dusting off unless we have an external drive to dump them to rather than having to uninstall them completely.
It's not that I'm likely to have a large collection anytime soon but it is something that I've thought about.
There was an article on the tech game site where some modders had put in a couple of SSD's to give more storage and get games to boot faster (by about 5 secs) but it was complicated and hardly worth voiding your warranty for.
Just thinking ahead!

i hope they don't make us have 'official' HD's be way to expensive here,i can get a 2TB hard drive for around $100AU.i don't see a microsoft branded one being that cheap.it would be nice if we could see how much space was left on the HD and a download history would be good too.i really hope they don't take long to make up their mind about the external HD.(i will be close to needing an external by about June).