To cut a long story short, here's the exploit I mentioned I'd found in the score submission forum, the one I suspect is going to be ruled out for high score submissions:
In Splash Garden, as you almost certainly know, there are a few orange-and-blue switches that spew out items when you hit them: on the first hit they give you a bunch of chips, on the second hit a bunch of stars, on the third hit slightly less stars, and for each hit after that, just one star. Just one star isn't really worth your while when you're NiGHTS, but considering that Claris and Elliot aren't restricted by NiGHTS' time limit, you can just keep hitting those switches as Elliot to crank an unlimited number of stars out of them, eventually giving you a ridiculous score.
"But", I hear you cry, "what about the bloody alarm clock? It kills Elliot!". Unfortunately, there seems to be a way around that in this case; if you head south-east from the Splash Garden start point, you'll eventually come across this switch in the "lake":
That rock directly beneath the switch is Elliot's ticket out of Clock Murder Land. As the next screenshot shows, it's quite easy to stand on that rock while simultaneously being in contact with the switch's lever:
...actually what you'll be standing on is the invisible "bounding box" around the rock - a lot of the random objects in NiGHTS levels just have chunky invisible boxes around them instead of accurate collision detection, these rocks included.
While standing on the rock like that, Elliot is simply too high up to be hit by the clock's ray of light: the clock can't "climb" on random level objects like these rocks (it just passes through them), and the part of its ray that can actually hit Elliot is below the height he'll be at, as this shot sort of shows:
...so while standing here, Elliot just can't die. You can keep jumping on the spot to trip the switch over and over.
But! After experimenting with this exploit to work out just how bad it could get, I discovered something I wasn't aware of: after about fifteen minutes of doing this, you just spontaneously die. Further experimentation revealed that there's a "master time limit" ticking away while you're controlling Elliot, and after roughly fifteen minutes the screen just fades out and you get a Night Over. I expect this applies to Claris and Elliot on all levels, though of course I've never run into it before.
So actually I was mistaken, you can't use this tactic to get an infinitely large score, but that doesn't really help matters much. In fifteen minutes you can crank over 30,000 points worth of stars out of one of these switches, 60,000 if you're in bonus time, which can still skew your scores significantly.
For example, on Course 1 you could use this exploit to get about 30,000 points to start off with, then become NiGHTS and get another 100,000 points for playing the level as normal, leaving you well in excess of the best "legitimate" score. Also, Course 4 currently has a high score that's actually *below* 60,000, so on that course you could just:
1) Free the Ideya to go into bonus time
2) Run out of time to become Elliot
3) Use this exploit to get 60,000 points
4) Finish the course.
So, you can probably see why I think this exploit should be a no-no for score submissions: it's just too tedious to perform. For the most part I'm happy to accept bugs and cheesy tricks because, for better or worse, they're "a part of the game", but I certainly don't think people should be expected to spend 15 minutes doing nothing but hammer the A button just to achieve a competitive score. :/
EDIT (01/02/2007): broken link(s) fixed.