The common description of Petrie's Pillar goes something like: "A shore dive for the beginner, with moderate currents and an average depth of 30-100 feet. The terrain is much like Andrea I and II. Large stands of Pillar Coral are found in the shallows along with schools of Blue Tangs. This site was named by Capt. Don as a wedding present for a friend." If you believe this description, you're likely to abort the dive before setting foot in the water! The waves from hurricane Lenny in 1999 destroyed most of the shallow corals. The shallows are now carpeted with algea covered rubble, several feet deep, making the entry very slippery and dangerous. It's very easy for a foot to slip between the dead coral, and twist your ankle in the process. If you attempt this entry, using you buddy for balance (and vise-versa) is almost required.
Getting down from the parking lot to the shore can also prove to be a little challenging, though not to the extent of the actual entry. You should bring along a pair of good solid shears, in case you need to cut away some of the thorn bushes. Walk down to the shore before putting on your gear. If you don't have a good sense of balance, you might have some difficulty. The path is narrow and a little tricky.
Before getting in the water, take a compass reading. There's a good swim over featureless sand flats after the rubble strewn shallows. One or two coral heads along the way can help validate your navigation, depending on your chosen heading.
So, why bother shore diving Petrie's Pillar? Well, it depends what you like to see on your dives. If you're into small stuff, the shallows here are excellent - on par (or perhaps better) than Tori's Reef. On the reef itself, you'll see a good coverage of hard corals and sponges.