rear wheel frustration

what does out of true mean? .....

How old is it? Did you get it from a Trek dealer? If you bought it from a dealer I'd take it in and talk to them about it.

When the wheel isn't aligned in a single plane. Basically it wobbles when you spin it.

I personally think that truing a wheel is as much an art as a science and some mechanics are better at it than others. I have the same wheels  and they have stayed true for the last year with a bit of riding (about 4000 miles.) If you got the wheel trued at the same place each time, I would be looking for a different place to do the work. If, after getting it trued somewhere highly recommended as a good wheel-building shop, it still doesn't stay true, then I might start thinking that the wheelset isn't the right one for me.

And yes, the Mavic Open Pros are great rims. My hubby has one on his powertap wheel and it has held up well to about 6000 miles (and he weighs 210) .

If my memory serves me right Bontrager had some sort of problem with their wheels this year. I am pretty sure my LBS told me that if I had any problem with mine just bring them back to them and they would give me another set without any questions.

Might worth asking them 

I'm new to this whole bike deal myself, but I had advice that you need to take it to someone who will retighten the whole wheel and not just make it "true" on a truing stand.   In your situation I'd be questioning the wheel and the person "truing" it up.  

I've got a rear myself that is wobbling and I've got an event this weekend.  Supposedly it should be a good wheel if tightened properly, but I'm also thinking new wheels and putting these on these on the shelf for spares.  My advice with new wheels isn't worth much, but I am considering the Neuvations due to some recommendations and reviews I've read... not to mention the $$'s they cost.  

Could the problem be with the spokes you have w.r.t. your weight?  I really do not know.  As for neuvation, I have some R28's with ceramic bearings on my bike and would not trade them for twice the price Mavic's. 

Neuvation, it seems like they have upped their price a bit w.r.t. the aero wheels to where I would rather go with a name brand (Zipp/Bontrager etc.).  I expect a price break when no LBS is involved!

Is it the same spoke(s) that are getting loose? Alloy nipples (if it has them) can have problems. Take it to a shop, should be an easy fix. As mentioned earlier, you need to look at the whole wheel, all spokes tensioned properly (not just the problem area) to have a wheel that stays true long term.

As for the Open Pro... great rim... but what are your goals with a wheel? Open Pros are nice and light. Great for climbing and accelerations. Not as aero as some of the low spoke count, high profile factory wheels.

I have Bontrager wheels and they stay straight even when riding on poor quality roads full of pot holes. 

Thanks everyone,  I took the bike to the LBS today (man am I happy I got the bike from them instead of online).  The mechanic there, who I've known for 10 years said that I should still be able to ride on that wheel and I shouldn't have to go out and get something new.  He is keeping it for a couple of days.. he is going to go over all the spokes and he will also use something called "spoke freeze" (I think that's what he called it) that keeps them from getting loose.  He is also "re-dishing" the wheel.  He seems to think that the wheels I have are good wheels and they should last me many, many miles once he has done the work.  He also suggested switching to 700x20 tires instead of the 23s I have to give me some more clearance as it is a tight fit between my wheel and frame so if the wheel gets slightly out of true again (which he thinks should not happen anymore) the tire will not rub against the chainstay and seat stay while out on a ride like it has in the past.

I may still get an open pro just to have for training rides and such. 

Does anyone have any recommendations for strong reliable wheels that resist going untrue for around $100-$150 (w/o cassette) that I can use for training rides or on the trainer?  If I were to get a wheel like that, I would not be concerned with the weight/aerodynamics of it... just strength.

That's exactly why my LBS mechanic thinks that after he works on it, I shouldn't have any problems.