Personally, I prefer the Tacho solution that our group PA-28 runs on.
If I fly for an hour at 90kn, the tacho shows about 45 mins. If I fly at 110, it shows about 65 mins. So I get more airtime for my money. If I was on hobbs/clock, I'd go everywhere at 110kn. I think of it as my reward for treating the engine with care.
The aircraft at a club that I frequent use the airswitch that Dude mentions. It activates at 40kn. I pay for my time >40 +10 mins ground time. The reason they do this is so that we DON'T rush checks & take care when taxying the old girls around a bumpy grass strip.