I think we've all used shepherd's hook stakes at some time in our lives.

Do they work? Depends on the soil type: sand, no; forest soil where there won't be a lot of wind tugging at the tent, so-so; any wind, they pull loose pretty easily - and since wind is often accompanied by rain, re-staking your tent can be a pretty miserable experience. (Oh, and mud - not very well.)

I quit carrying shepherd's hooks as soon as stakes with a Y cross-section became available. For the soils I camp on (Ohio Valley forests), they hold great and are hard for the wind to wiggle loose. I haven't found enough difference between titanium, steel, and aluminum in use to matter; there is a small weight advantage to titanium and aluminum, but it's offset by higher cost. Right now, I'm using aluminum Y-stakes because that's what came with the tent and they haven't let me down yet.

As far as how a shepherd's hook holds hold up to a rock used as a hammer: depends on the size of the rock and the enthusiasm of the user.

Speaking of rock, if you hit a rock or a root while trying to place a shepherd's hook using any pressure (for example, pushing with the sole of your boot), they'll do a great job bending and a lousy job of straightening back out.

I suppose I've wasted money on worse things than shepherd's hooks...