Losing Layers

Start a new photoshop document.
Create a black square in a new layer. Use a selection rather than making the square using vector shapes.
Duplicate the square as a new layer.
Set the opacity of the first square layer at 10%.
Set the opacity of the second square layer at 9% or less.
Now you have the white background and the two transparent layers.

Now, try to right-click the first square. A pop-up will appear telling you that you can select either the square or the background. This is fine.

Now, try to right-click the 2nd square (the one at 9% opacity) the pop-up will say you can select only the background.

Having Auto-select ON on the Move tool wont help you select either one of the two squares. You will say, that's fine, i still have the layers palette, i can select the layer from there.

Now imagine the following scenario.
A layout for a web-portal. 1000x1500px. You got more then 100 layers there. The layers palette is very messy: unnamed layers, wrong order, etc.
You can rely only on left clicking or CTRL + clicking for selecting a layer. Suddenly you lose one layer. You can still see it but because it has an opacity below 10% you can't actually click it anymore. What are you supposed to do, try hiding and unhiding every layer from top to bottom to get to that?

Well, no problem.
Select the Move Tool, have the Show bounding box option ON.
Go to the layer palette and select the background.
Now push ALT + [ or ALT + ] to quickly navigate through layers.
You will know when you have the right layer selected because you will see the bounding box.

PS: and another useful tip.
when reaching 100 layers in photoshop you automatically gain a new layer, as a bonus