My mom's original imac g5 had an external firewire isight camera. she's got a big loft and a lot of neat stuff there and frequently tried to point the camera to show me something.
So I bought her a 25 ft firewire cable, and a firewire coupler. (yes, they make them) Now she can get up and walk over to it etc.
Works fine for the camera. I suppose you may get slower file copies etc though if it gets errors due to cable length or cumulative interference. Finding said cables and couplers though is a little bit of a trick, but you can obtain them, they're out there. I carry a white isight (6ft) firewire cable in my bag due to its small size and low weight, and I think I've seen it doing slower file copies than a standard cable, but it still works, no refusals, no random disconnects or stalls.
On a related note I've used a whole boxfull of usb cables and extensions to get a usb run on a wireless adapter up and out of a basement up three flights of stairs, and that too worked nicely. So I think it's a "maximum length we GUARANTEE to work is ..." more than a law. Though I do remember back in the days of scsi you most definitely had to be careful with cable lengths.
