Don't have one and never would there are many other options that would offer better off-road ability, cost less, get better fuel economy, and have a better aftermarket base if you want to upgrade anything.
The H3 is known to be unreliable, only rated as a 5/10 this score is based on trending the past three years of historical initial quality and dependability data from J.D. Power's automotive studies, specifically the Vehicle Dependability Study (VDS) and the Initial Quality Study
If you just want an SUV that still looks cool, consider the Toyota FJ Cruiser. It offers off-road abilities but also boasts better fuel economy (16/20 mpg) and costs nearly $10,000 less than the Hummer. Another great off-road SUV is the Jeep Wrangler, which performs just as well as the Hummer, saves you another $2,000 off its price, comes with the same rugged styling and has a marginally better fuel economy.
As much as I hate Jeeps I would say going with a new 4dr Jeep Wrangler. The aftermarket is crazy and for some unknown reason these things hold their value like no other vehicle.
This is a list of some of the issues the H3 Hummer is known for yeah some may seem little, but add things up and any issue becomes a pain in the ass.
Airbags: The airbag warning light may no go off due to a faulty seat belt tension sensor in the right front seat belt retractor assembly.
Check-engine light: The engine may run at lower power and the check engine light may illuminate if the engine was started with a weak battery.
Coolant leak: Coolant leaks from the reservoir when vehicle driven at increased angles such as off-road requiring replacement with revised component.
Electrical problem: When using a portable music player (e.g. iPod) there may be noise in the car's speakers whenever the vehicle's power adapter is used and a ground loop isolator (from Radio Shack) is required between the device and the power outlet to prevent the noise.
Electrical problem: The trailer wiring harness can contact the muffler and melt rendering the circuits inoperative.
Electrical problem: The DVD monitors in the front seat headrests may quit working because the video feed cable comes loose requiring installation of cable clamps.
None: There was a campaign to replace the jack with a more durable on for some early model year vehicles.
Tail/brake lights: The taillight housing may come loose requiring a redesigned retainer.
Water pump: There was a campaign to replace the rear window washer pump.