Does the live USB drive act like the Live CD?

My understanding is that when I use my Ubuntu Live CD, there is no permenant storage, that it creates a filesystem in RAM, so that when I turn off my computer, absolutely nothing is left behind. I consider this a feature, for example if I want to access home banking, I know there is no key logger installed by some kind of drive-by download from a previous session.

However, the Live CD sometimes feels a bit slow. Based on this:
http://sourceforge.net/apps/trac/unetbootin/wiki/guide
It looks pretty easy for a newbie to create a live USB drive without any 'scary' command lines.
If I do this, is my USB like the Live CD? That is read only, with writes restricted to RAM? So basically mal-ware-proof? Assuming nobody corrupted my BIOS?
Or is it more like Linux on my computer? So, for example my FireFox cookies are preserved? Not horrible, but different expectations.