I have talked/emailed privately with some of the frequent posters on the MLP/GP boards. It is more difficult to value the GP's than the MLP's. The market was, and you could probably say, still is using yield. The truth is that there are a multitude of different and better ways to analyze them. The growth leverage they possess, the capital structure(taxable or non-taxable entity), amount of debt/leverage at the GP, the existance of lack of operating assets at the GP level, the growth prospects of the MLP, the average cost of capital for the MLP, etc etc etc. Its not as easy as saying they should all trade at a 3.00% yield. Most of the public GP's have nice niche. Kinder Morgan has the CO2 tertiary recovery operations, Enterprise has a near monopoly on the Mont Belvieu NGL hub etc etc.
I personally like Crosstex and a quasi MLp, Copano, because of management and growth prospects. Lehman highlighted the growth prospects at XTXI are not nearly diminished as the market has seemed to think. These are great opportunities. Copano has huge growth built into the existing assets yet the market does not reflect all of it into the price. It is trading at a lower yield but remember it has no GP to pay, and they are still small, have a great balance sheet and a huge coverage ratio. They could notch the distribution up for a year or two (albeit at small increments every Q) without ever having to make any acquisitions and still be in great shape a year or two from now. Right now the market is saying, show me for both XTEX/XTXI and CPNO and I think they will both come through strongly.