Some people need internal floppies, but the only time I've ever needed it was once when I wanted to take something to Kinko's and my local one didn't have access to the net.
It's more important, of course, to have a floppy on a PC because of boot issues, such as the inability of many PC operating systems to boot off CD, like the Mac OS does. And in Linux, where 'boot disk' is often still paramount, it's even more important.
If you're transferring files back and forth from work or school via floppy, that too might be a reason to stick... BUT...
USB floppy drives exist, they cost around $79, and the ubiquitous Zip drive has almost replaced em anyhow, and USB Zip drives are now out..
My fiance was a PC user before I convinced her to buy an iMac for her new computer, and she was very skeptible (that's kinda like spektacle, I mean skeptical) about the lack of a floppy, because they're such a big thing in the PC world. But she's never even needed it once and she's a teacher
I'm not trying to convince you to buy one, btw.. just giving a different point of view.. for some people floppies are entirely necessary, and I can certainly understand the need for them.
BTW, why an 'internal' floppy specifically?