I use it routinely when browsing on a laptop without my scroll wheel mouse...it gets me down the page a lot faster than using the arrow key and it's very conveniently located.
I think IE may actually have been the first one (web browser) to do it. I remember at that time at least, that this feature showed up in IE and Outlook around 1998, and I remember really liking it, and I don't remember that Moz or Netscape had it at that time. Could be wrong, though.
I don't see why it's a problem that it's there. It's just another way to do things that may be intuitive to users. It's really particularly nice in mail applications, though to be honest. Because in most mail apps, it not only advances to the beginning / end of the message but an additional press of the same key goes to the next / previous message.
So between shift and space you can read through your whole inbox while doing other things... Get used to 65-70 hour work weeks and reading your mail at 6 in the morning while still trying to wake up and waiting for your coffee to be cool enough to not burn you and defrost your fingers from the subzero temperature outside and little things like that make you really happy....
I use it routinely when browsing on a laptop without my scroll wheel mouse...it gets me down the page a lot faster than using the arrow key and it's very conveniently located.