I have a 2003 HCH with 110K miles on it. And I too have serious issues with the IMA and check engine light turning on/off randomly, shocking, I know.
At the end of December '09 the IMA light came on, so I took it to the dealer and they charged me a ridiculous amount of money to update the computer. I drove no more than 14 miles down the road and both the IMA light and check engine light came on. I immediately called the dealer but unfortunately I picked my car up from them at 4:55 PM and the service dept closes at 5 PM... sweet. I called the next day but they couldn't give me an appt. until after the holidays. The day before my appt. in January both lights randomly went off, so the dealer told me not to come in and that the lights probably came on because "the computer just needed to reset itself"... riiiiight.
The lights stayed off for 3-4 weeks, and have been coming on and turning off randomly since. Usually they are on for 7-10 days, then turn off for a while, then randomly come back on. One time they were off for a whole month. Sometimes both come on, sometimes only one. I haven't noticed any difference in the car's performance whether the lights are on or off, so I've avoided bringing the car back to the dealers, mainly because I'm stubborn and angry. Now that my car is at 110K it needs an oil change, and just the other day the IMA, the check engine, and maintanace required lights all came on at the same time.... trifecta.

Any advice for what I should do? Continue to ignore my dashboard, which seems to have more neon lights flashing at me than a street in Vegas? Or take it to another dealer for the oil change & problematic lights?

Oh, and I almost forgot - if I drive for more than 15 min, then stop somewhere and turn the car off - when I try to start it up again after leaving it for any less than 1 hour, I have to rev the engine while trying to start it, in order for the car to actually stay on. Without my foot on the gas, the RPM immediately drops to zero and the car stalls.... anyone else have this ridiculous problem too?