This is a photo I took the other day at the zoo.Take alook at the exif and judge for yourself if Built in IS works.Its not a perfect picture but it was handheld at 450mm. I am not saying that IS is perfect or better than in the lens but giving you some info to go on.
Camera make: SONY
Camera model: DSLR-A100
Date/Time: 2007:01:27 13:19:25
Resolution: 536 x 800
Orientation: rotate 90
Flash used: No
Focal length: 300.0mm (35mm equivalent: 450mm)
I'm just being needlessly pedantic here, but it was actually handheld with the lens at 300mm, not 450mm. 450mm as you point out is what you would use with 35mm film/sensor to get the equivalent field of view, but the focal length is still 300mm.