It's not really live rock and it doesn't perform the same function as live rock. If you only want it to look like rock, then it works. There are a few people here who have done it with Mike aka Texreefer being the most experienced at it. He has a tank build thread going in the general reefkeeping forum here:

http://www.maast.org/forums/showthread.php?t=40266

This is his second tank using the foam and he always does a great job. If you do a search here on Maast, there are several other threads on foam use as well.