WDS
When I first moved in to our house in 2001 the lawn was pretty well taken care of. My first year or two I had no idea what I was doing so I never fertilized or weeded. I just mowed once a week. Dandelion and crabgrbutt was going wild during this time.
My neighbor usually fertilizes religiously, and our yards are small enough a single bag covers both of our yards, so he supplied me with fertilizer (spring weed prevention fertilizer, etc, i think we fertilize 3-4 times a year).
After two cycles (2 years) of this, the crabgrbutt population was cut down alot, and dandelion population got to the point where I weeded whenever I saw yellow flowers and usually had only a dozen or so to pull at any time. This is pretty much where I'm at now. My yard is really nice and full, with very little crabgrbutt or dandelions, and all I do is fertilize whenever my neighbor reminds me, mow every week and pull dandelions when I see yellow flowers.
The boulevard patch of grbutt is full of dandelion's though. I almost always forget to fertilize there so it's not controlled as well.