I bought Dan Harrison's OBDII tool about a year ago (both the PC and the Palm versions), and though it does a "decent job," it is far from perfect, and does not reset the service light on my 1998-S70. I do a fair bit of computer programming myself, and the program used for the interface is rather immature IMHO.

I am actually considering just going out and getting another one, in particular the one at http://www.obd-2.com which is indeed supposed to reset the Volvo service light...but I have not tried it either!

If it weren't for the weird plug used for the OBD-2 connection, and the slightly unusual bit rates, I would just do one myself! Oh well, maybe with OBD3 ISO will do something logical and actually use an industry standard connector like IEEE-1394, USB, Serial/Parralel, RJ-45, or any other... I mean really:)
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Two '98 S70 GLTs. DawesDevice (@ 9.5 psi), Dawes A/F meter, boost guage & pod, IPD anti-sway bars, IPD engine plate, Bilstiens, IPD strut tower brace, IPD torque bushing replacement, Boston Acoustic speaker upgrades, Volvo 6-CD changer