Some of the LaCrosse weather staions use a reed switch to counts tilts of the "see-saw" in the rain gauge The Whirlpool Duet clothes washer uses a reed switch to measure how much water has been run into the machine - it gives 815 pulses per gallon. Both of these units have magnet(s) that operate the reed switch as they go by. The engineers obviously expected an "acceptable" life from these items (although my definition of "acceptable" is probably 10 years longer than theirs ;-)
Still hoping to get back to me PICAXE-based irrigation controller, which uses one of the Whirlpool flowmeters to measure the amount of water delivered. I've acquired ideas for keypad, menu, realtime clock, etc, from Forum postings but haven't gotten beyond the "bits on a breadboard" yet;08M interrupts at 8MHz can keep up with the flowmeter at a flow of 4 gallons/minute and still update a serial display(4GPM * 815 pulses/gallon = 3260 pulses/minute or a little over 5 pulses/second). The bigger chips (14, 16, 28) are waiting for the extensions.
Spinal fusion surgery really slows you down - even 6 months later...
John