Lawrie switched from a Canon SLR to Panasonic DSLR body over Christmas, and was looking to sell off his old Canon EF lenses. I picked up his Canon 75-300mm f4-5.6 USM Mark II for a good price.
It's not the best lens ever made, and the optics aren't much (any?) better than the kit lens, but it sure is long. I wanted something with a good reach, and this sucker has that in spades. At 300mm, the visible area is about 6? across (if I hold my arm out in front of me, with my hand up and fingers together, it's about 3 fingers across).
There is noticeable chromatic aberration, especially in bright photos with high contrast. But, for a lens to grab a mountain from over 100km away, it ain't half bad at all. It's certainly no worse than the kit lens.
It's not a fast lens, either, meaning that I'll need to use a monopod or tripod in low light scenarios, even moreso at the 300mm end of the lens. But, that's not bad since I have a handy dandy monopod.
The lens is far too long to be a regular walking-around lens, but will definitely come in handy for shooting far-away things, and has a decent macro at 1.5m, so I can take nice closeups of stuff without cramming the lens into whatever the subject is. It doesn't come close to the 28-135mm USM IS lens, which has a more normal range and much nicer optics (and I'm still saving up for that one, too).
I've taken a bunch of test photos to see how it behaves at the extreme ends of the range.
Here are some samples of a scene from my back door. The first shot was taken at 300mm on the new lens, the next at 75mm (the wide end of the lens), and the last one taken at 18mm using the kit lens.