What's your tipping policy?

I'm a very inconsistent tipper. Now more than ever, I'm trying to restrict what I spend, so I think about it frequently. To make it more confusing, I must not know all the rules. I've had the conversation with people over the years, and everyone has different ideas of what's an appropriate tip for a given situation. Here are the categories in which my confusion lies:

1. Take-out Food
   This is what got me started thinking about it again today. With our first attempt at Taco Soup brewing for dinner (and more than a few lunches) JC and I caved and enjoyed Lenny's for lunch. I thought I'd pocket the delivery tip and go pick it up myself. Online, I was confronted with a tip box at the end. Huh? Why else would I pick it up? Call me crazy, but the main reason I'm picking it up is to save a couple of dollars on delivery. I left it blank, but surely felt some guilt about it. Paying by credit card makes it worse, since that tip line shows up, looking all blank and lonely. Sorry, tip line, but you're sleeping alone tonight. Am I the only one who leaves the tip line blank for take-out??
   
   
2. Delivered Food
   JC and I have disagreements over this. I used to tip 15%, as that's what I thought tip practically translated to (I believe it's Finnish in origin....) Anyway, we ordered with a few friends one night and I figured the tip was about $20 for bringing food from 5 blocks away. After a few awkward glances around the table, we figured tipping for delivery is more of a set-price thing, loosely based on (distance) x (the number of bags delivered) / (the temperature) + (Preciptation) / (Mode of Transportation)... and somehow pie gets figured in there (the dessert, not the mathematical constant, which would be too easy).... Now it's "ahhhh, give him $3". I'd like to see that tip calculator.
   
   
3. Sit-down Food
   My general feel here is 15-20%. It's rare that the tip is ever dependent on quality of service, though if someone goes above and beyond, we try to be generous. Lousy service still gets at least 15%, but as they say, "you can't put a price on talking smack behind someones back." - author unknown
   
   
4. Service for something included (ie. leaks repaired by the landlord)
   This might make a difference in the type of apartment you live in. If you're in a full-service doorman type building, it might be expected that you tip anyone who comes into your apartment to do work. Of course, if you got it like that, props to you -- it might be in your nature to tip anyway, and this point is moot. In the past month we've had no water for a 36-hour span, and no heat for the same amount of time three days later. You can rightly assume that we're not living with the Jeffersons. We generally don't tip for landlord service, but we'll offer coffee/coke/water, etc.
   
   
5. Service such as furniture delivery, man with a van, etc.
   Another confusing one, as you've generally paid a shipping cost for your item, possibly a large amount. So how much more do you tip for a service you already paid extra for? I figure you can probably size up number of people * bulk of delivery * time spent in your home... In my experience, this usually comes out to between $5 and $15 per person.
   
   
6. Taxis
   A co-worker from around 2000 had some formula in his head which was something like "I round up until it hits $10, then I round up and add a dollar". I thought this was pretty measly (consider a trip that totaled $9.70), but with small totals and cabbies that don't really deal with change, this is usually my least consistent place to tip. Granted, my taxi days are few and far between now, but occasionally it happens. My preferred method in the past year has been to use a credit card, and just tip a dollar or two on a short ride. No change, no fuss, and no ATM charges...
   

Do these "rules" sound way off? Are there exceptions to the rules that I'm missing? I'd love to hear your thoughts (...um, unless you're the cashier at Lenny's. :)