I am a bit addicted to Google Earth, actually it is helpful at times especially the street views when you are headed somewhere for the first time, or sometimes just to get a different perspective on different places you have been. Google Earth also has historical imagery allowing you to see not only the current published image, but previous ones as well.
A while ago I was playing with historical imagery and captured these images of the Swan and Dolphin taken between February 1994, and May 2010. You can also see how Google Earth imagery has improved over time.
Click on each photo for a larger view or visit the entire set on Flickr.