As far as I have seen, live rock from the stores around here is just too expensive for what you get. It all looked like overpriced base rock. I have not purchased Marco rock but am very much considering it when I finish my tank build. First, it is a lot cheaper than live rock that is filled with water, you are essentially paying to ship a lot of water. Second, it looks to have better shapes than a lot of the live rock I have seen being sold. Third, you end up losing a lot of the live that was on the live rock in the first place if it was not handled/shipped properly.
My thought at this point is that I will buy 50 lbs. of Marco rock for my 50 gallon. I will then buy/trade for 10 lbs. or so of nice live rock to use as seed rock. It won't look all that great at first but like in most of reefing, all good things come in time.