I usually take this lens when I need something smaller and lighter than the 100-400. My son and I both took it to Florida on vacations and it's very sharp.
Here are some shots taken with it on a 30D:
1/60s f/5.6 at 300.0mm iso200
1/160s f/4.0 at 70.0mm iso1000
1/1000s f/5.6 at 300.0mm iso1000
1/500s f/5.0 at 200.0mm iso400
1/640s f/8.0 at 70.0mm iso200
1/500s f/5.6 at 300.0mm iso200