Is it possible to use an Android phone in "disk mode"? If I connect an iPhone to a PC it is not possible to copy files between the PC and the iPhone. I would like to be able to do this because it would be useful.

What happens if I connect an Android phone to a PC? Do I see it as a disk or is it similar to the iPhone?
Absolutely, and it's very easy.  This is the procedure for my Samsung Galaxy S; other phones may be different:


Plug in the USB cable and a USB icon
appears in the notification area at
the top of the screen.
Pull down the
notification and tap "USB
connected". 
Tap "Mount" on the
dialog box that's displayed. 
Two
removable drives show up on my PC;
one for the built-in flash memory,
and one for the expansion SD card.