The answer is based on what you want to accomplish and your emotional connection to the money. There are two extremes - and I've seen them both.

1. Wow I made some money let me take it off right now "before I lose it" - Fear related Cashout.
2. The bigger my bankroll the better player I am and the more buffer I have so I will essentially Never Cashout. There are people with thousands online who have never taken a cent off. - Fear related NON-Cashout.

I read Killer Poker Online - or most of it. I'll read the rest today. I can't say I'm a big fan, but my mentality is different than his.

Here's my recommendation and/or questions:
1. Are you sufficiently bankrolled for the stakes you are playing? (See bankroll management) Most new players are woefully underfunded. If you aren't then leave the money on as a realistic buffer against loss.
2. Is the amount of money you have online (whether out of your "pocket" or in "free" winnings or both) something that you are uncomfortable with "gambling" with? Some people can lose $200 no worries but if they have $2000 online they might play scared because it's an emotional problem. Act accordingly.
3. Do you want to increase in stakes? If so then you need more money.
4. Do you like looking at it online. Does it make you feel good, motivate you, and help you play your best poker. (This is often the case where more makes you feel more confident and play better.)

You need to do a quick review of your logical, emotional and Poker requirements and make the best decision for you. Here's what could happen:

1. You leave it on, lose it all and feel like crap.
2. You leave it on and it propels you to greater glory.
3. You take it off, spend it, and feel good. Your remaining money online is enough.
4. You take it off, spend it, lose the remaining money you have online and can't afford to put more on, so now you can't do something you love. (play poker)

I think that covers the most likely scenarios. There is one where you leave it online and just sit idle for ever - but that's unlikely.

Don't follow any arbitrary rule. Do what you think will help your poker and your life in the best way possible. I would say Vorhaus' recommendation isn't bad. It builds your BR and gives you some emotional payback.

Here's another option, take $50-$100 off and spend it on your family or wife. Because they are putting up with you spending all your time staring at the computer and insisting that you have to concentrate. What's their payoff? This may be it.

Good luck and nice job. I'm going to re-read (and finish) Vorhaus book and see where I can get some value out of it.