my cessna 172rg has a o-360 in it which exhibits the same behavior described in the original post.
my experience has been
- of course keep it lean on the ground
- keep it lean on final approach and moreso after landing.   (this is the biggest factor after ground leaning but it means you have to change mixture on a go-around)
- iridium plugs didn't help
- when it's a problem and I dare take off, it's usually cleared by the departure end of the runway
- when it's a problem and I don't dare take off, it takes 2300 rpm for about 45 secs to change anything.
- you can tell when the problem is gone because the egt will come down in line with the other cylinders.

Colyn