We (RescueTime) did TONS of A/B testing on pricing/plans, to very good effect. People seem really hesitant to do this for fear of pissing off customers, but we didn't get any complaints. A few folks noticed, and we'd always honor the lowest price they saw if they were part of the experiment.
We mostly only had enough volume for solo users, where we tested anywhere from $4-$20/month for an individual account. Found VERY little difference in conversion anywhere below $10, with a big dropoff thereafter. Pretty remarkable that conversions change almost not at all between 9.95 and 3.95/month.
Our volume for business signups wasn't super high at the time (that's since changed-- go RescueTime!), so we didn't fiddle much with that.