Helping people with computers... one answer at a time.
It's tempting to think that simply copying a bootable install CD to a USB device would work. Sadly, it's not that simple.
I'm thinking of buying a netbook with no built-in way to read an installation CD if I want to add other software. I expect that I can simply copy the contents of any such CD to a USB memory key, using another computer, and install from the key. Can I safely count on that working, or are there still any installation routines that expect a physical CD drive to be present? Can you see any other problems I might encounter?
No, you can't count on that working.
It'll get you 99% of the way there, but that last 1% is a deal breaker.
What you're describing will work for many applications that don't require you to reboot from their installation media.
The problem is that many, specifically operating system installation media, require that you reboot from the media.
Simply copying a bootable CD's contents to a USB drive does not make the USB drive bootable. It copies everything except the part that makes it bootable.
That means that if you're ever faced with a "bare iron" reinstall - one where the hard disk in your netbook is empty, you have no way to boot from any installation media.
Now, there are various and sundry tools out there that you can use to create a bootable USB device, and even use an arbitrary ISO image of a CD to boot from. Most of those that I've run across are rather geeky, and not really for the average user. (Search for things like "bootable iso to USB", for example, and you'll get plenty of discussions if you're interested.)
My recommendation is actually much simpler, and something anyone can do.
Get a USB CD/DVD drive.
There are plenty of choices.
Making sure that your netbook will check for a bootable USB device first, when you need to boot from an installation media such as an operating system boot disk, just connect up the USB CD/DVD drive and you should be good to go.
No geekery required.