Like to remember where a particular image was taken? If the camera you're using doesn't automatically include location data in your photos (or if it gets it wrong!), you may be stuck adding that information into iPhoto yourself. Luckily, though, you don't have to do it one picture at a time, so here are a few ways to make the process easier.
First, you can select a whole mess of images and then edit the location data for all of them at once. To do that, either hold down the Command key as you click on photos to select multiple ones, or click and drag to draw a box around a series of images, which'll select them all.
After you've got your group selected, hit the Info button in the lower-right corner of iPhoto's window, and then type the name of the place you want to assign those pictures to in the location box.
That's neat! Secondly, if all the images you want to add locations to are in the same event, you can just edit the event itself, and it'll apply the location to all the photos within it. So click on the event in question, press the Info button again, and then assign your location in the lower right, same as before.
Finally, you can also copy and paste location data, so you don't have to select the images you want ahead of time. This is by far my favorite method—it's Melissa Approved™! To do it, select one photo that already has the proper location and hit Command-C (or choose Edit > Copy). Then select the image or images you'd like to mark as being taken at that same place, and choose Edit > Paste Location.
Handy! Nifty! Additional third adjective! By the way, do you think we can get Melissa Approved™ to become a thing? I guess I'll need to think of more things I approve of for that to happen.