It's true that Ctrl+Alt+I will bring up the Image Size dialog, which actually shows you the size of your image canvas, or the overall image size.
If you want to get the size of just a single layer's contents, (which could be very different from the image size), Ctrl+Click the layer's thumbnail in the Layers Panel to select all of that layer's non-transparent pixels. Now look at the Info panel to get the layer content's size in pixels...
John M:
All of the vim with none of that annoying vigor.