As of 3 Feb 2001 I have seen 3 flashes so can confirm that the predictions do appear to be accurate in terms of timing though perhaps less so for brightness. One potential daylight event, which Heavens Above can predict, proved negative.
By now I have seen many Iridium flares, including several -8 events, though as yet a daytime sighting has eluded me. The Heavens Above predictions appear to be very accurate and also reveal that for the latitude of the UK they can be seen at any time during the night for the summer months. With the greater chance of some decent clear nights there should be plenty of opportunity for sightings.
Several friends have now seen flares too, either in my company or elsewhere using Heavens Above predictions. The general comment has been that the flares are an impressive sight, coming seemingly out of nowhere, and given that they are in fact quite common, some surprise that people have not seen them by accident. It's all a matter of being in the right place at the right time.
My first attempt at photographing an Iridium also shows what is possible, as the following picture reveals. It shows satellite no. 45 brightening to a predicted magnitude of -8 then fading away again as it travelled from left to right through the constellation of Leo.
Iridium 45 flare in Leo, over Wijk aan Zee, Netherlands. 12 May 2001, 00:14:18 CET (summer time). Predicted magnitude -8 (the brightest possible).
Exposure of 40s with 50mm lens at f/2 on Fujicolor 200.
The satellite appeared in the WSW at an elevation of 36º and was travelling from south to north, left to right across the field of view. The star Regulus is just below centre of shot and the sickle of Leo stretches up to the right.
The camera was supported on a rather wobbly litter bin, which explains the shaky appearance to the satellite trail - of course the actual path across the sky was a dead straight line.
At times other than when they are reflecting sunlight directly at the observer, Iridium satellites have a brightness of about magnitude 5 or 6. This puts them at the very limit of visibility with the unaided eye, but they would easily be visible with binoculars or a telescope if you knew where to look. I have followed a couple of satellites with binoculars following flares and confirm that they can be seen, and even in the photo above you can just see the faint track to the edge of the picture.