I have a Canon 30D with a 100-400 4.5-5.6L IS Zoom. The canons have 2 IS modes 1 vertical and horozontal IS and 2 for vertical only.
I use mode 2 on a ball head tripod which is just tight enough to smooth out my movements as I pan. I find I get better shots with this combo rather than freehand for BIF. I use AI servo mode and I lock on the bird as it approaches by half shutter press and then only fire at 5 frames per second just as the shot starts looking good. I find that the patience to wait is the hardest part for me. Also with the 30D I think it is important not to autofocus til the bird is close enough so you have a good chance of it being covered by one of the focus points. I use ISOs of 320 or 250 mostly and usually Aperature prefered of 7.1 or 8.0 which is my lens sweet spot. It also usually results in a shutter speed of 1/640 to 1/1000 in daylight at the beach. Also since I am using a slightly smaller aperature than wide open I feel I have a little more wiggle room with focus.
I shoot plenty of bad shots.
EXIF for these shots:
1/1000 f8.0 ISO320 400mm
1/1000 f7.1 ISO250 400mm
1/640 f8.0 ISO320 400mm
1/1000 f7.1 ISO250 400mm