Quick! -- What time of day was that photo taken? Was their any exposure compensation used?

You can find out this kind of thing in Aperture with a single key press. Put the cursor over the image (or thumbnail) and hit T. Up will pop a little overlay that gives you some information about the image. Hit T again and it will go away. It's especially useful in full screen mode or any view with all thumbnails because you don't have to make any workspace changes and then undo them again.

Here is a full-screen image with the pop-up showing:

For this image, the pop-up looks like this. It is only as big as it needs to be to display the information that is available:

In theory the pop-up should change as you drag the cursor about over different images, but I have found this to be unreliable. So I generally hit T then T again to make sure it has gone. Apple calls this an Image Tooltip, but that is a rather odd name. It has nothing to do with tools or tips. Metadata Quick Look or something like that would be more meaningful.

The information it displays is customizable too, and that makes this an even handier tool. You will find the controls for this in View > View Options (or hit command J):

It's the last one. All you can do is to set the metadata set that is displayed by selecting one from the pop-up. Clicking the checkbox is the same as hitting T. You can enable the tooltips and see what effect the different metadata sets have with the window open.

Also on here are all the other settings for metadata display for both the viewer and the grid (thumbnails) and the list view. I choose to display everything Over thumbnails, but that doesn't really mean that everything overlays them because there isn't enough room. Here is a thumbnail with the display set to Over:

and here is the same thumbnail with the display set to Below:

The badges get their own space in the Below view, but the other data is always below. Show Labels will prefix each item of data with what it is, such as "Image Date". I keep this turned off since it just uses more space.

To change what the metadata sets such as Tooltips - expanded actually specify, you have to press I (uppercase i) to get the inspector and then select the one you want to change:

Then when it has been selected, you can edit it, rename it, or duplicate it, or create a completely new set:

If you chose to edit it, you will get a display like this:

You can remove items with the little symbols, or add them by clicking the checkboxes in the lower part of the panel. And you can change the order of the data by dragging the metadata labels.

I have my metadata views set up so that I have Viewer - Basic normally overlaying the image. What this means is that I get badges only and they are on top of the image. This allows the image to be as big as possible and have almost no clutter.

If I switch sets with Shift Y I get everything (Viewer - Expanded) below the image:

For thumbnails I can use Shift U to switch between the sets. Again Grid - Basic overlays the badges but I also have it set up to show the size of the image in pixels and bytes. This is small data and fits easily:

Grid - Expanded overlays the badges too, but puts other data below the image. I display keywords and captions in this mode so I can see how far I have gotten in adding that data to my images:

Although the controls are a little spread out, the metadata viewing capabilities of Aperture are pretty good. The only thing that I wish I could do that I cannot is to have more selections for the placement of data. For instance I would like to have metadata on the left or right side of many images. I have the screen space and it is black, but Aperture only puts the data it at the bottom, so shrinking the image size.

Tags: Aperture, Metadata Views, Workspace