I used to be a staunch every 5k-10k mile rotation guy but after many, many years and miles I base rotation on an as-needed basis.
Most of my driving these days (or at least over the previous 5-10 years) has been highway. I usually don't schedule it on mileage but on visual wear or if I can feel unbalance. I currently have 36k miles on the stock tires with no rotation although I probably should have had them balanced and rotated at 25k-30k. The tires on my Mustang have gone 24k miles with no rotation and show no uneven or irregular wear.
I believe that scheduled tire rotation is a lot of hype and unless you get it free, then I wouldn't bother. If you need it more often, then you need to look at your suspension. The cost of rotation and balance over the service life of your tires could, in many cases, pay for a pair of tires so what are you really saving?