Limiting Kids' Computer Time?

Bibu asks: "As a parent of three, I have to spend a lot of effort to keep my kids away from the computer. Until now, we had a Linux box in which a little cron script would just shutdown the machine after half an hour, when the kids were using it. Does someone on Slashdot have a fancier solution? One that keeps track, controls the total time per user per day, and would warn the user of the upcoming deadline (e.g. in five minutes their time is up)? Since we just moved to Mac OS X, solutions for that platform are preferred."

Re:As a child of parents who used to do this...

[miyako]

I agree with this. My father used to impose rather insane and completely random time limits on just about everything, and the only thing it did effectively was build up anamosity.
For example, computer use was limited to 10 minutes per day. I should point out that this was inclusive of both recreational and academic use. Have a paper due tomorrow that you need to type up? Hope you can type the whole thing out in less than 10 minutes (minus the two to three minutes it took windows to boot up, and the additional five it took for word to start). The internet was pointless as we had an old modem (probably 14 or 28k) and it would take longer to actually sign on and load a page than we were allowed to use the computer.
In the end my Uncle bought me a computer and pretty much told my dad to fark off and gave it to me dispite is oppositions. I can still remember waiting until everyone else fell asleep at night and sneaking out to hook up my modem to the phone line, using NetZero to connect when it was still actually free to do research for school or ssh into the schools server to write and compile my programming assignments.
In the end, all the rules really made me learn was to hate my father and to have a sort of innate gut reaction that most rules are completely asinine (a gut reaction that actually seems to pan out most of the time upon fruther logical examination) and only exists as something to get around.
Remember, it only takes 1 or 2 asinine rules imposed on your kids before they'll assume ALL of your rules are completely without a point and ignore everything you say instead of just the stupid stuff.