What if Harang is really good in 2006 and 2007? Sure, he'll make watching every fifth day bearable, but where does that get us as a whole? I'm not saying deal him no matter what, but if you can get a teams top 2 pitching prospects for him, and your scouts tell you they are the "real deal", then you should pull the trigger, IMO.
Can't have it both ways. There is no short cut to rebuilding and doing it right. Have to completely gut it and hope that all of your talent develops at once, hope everyone hits their "prime" in 3-4 years and is still relatively inexpensive so you can add other pieces if you need to. I think Harang is a good, young pitcher, but he's not so good that you keep him for 3-4 years as he starts costing real $$$$, instead of trading him for younger pitchers who's development curve is more in line with your timeline to compete.