Well from having the lens for five days with 3 days shooting 'properly' rather than mucking about in the garden etc I love it and given the extra spare cash would consider it in a heartbeat. My other consideration would be the 70-200 F/2.8 IS and a x2 converter but hey I don't have that much spare cash right now
The three days shooting where a Sunday at Leeds Castle where they had a jousting display on amoungst all the other stuff including a Falconry display which I went back to the day after when it was much quiter and finally the third day was at a British Wildlife park in Surrey.
Weight:
In my hands it felt about right not unbalanced with the 450D at all and I quickly got used to it. In the rucksack on my back I couldn't tell much difference
Zoom:
In use the zoom is really easy to use (push pull), it did get a little bit of stiction if you wanted to just ever so slighty adjust but I found after a while I would use my fingers on the join to good effect.
Things I had to watch out for are in crowds if you extend it all the way along with the hood you could end up ****ting someone in the head if you're not careful, thankfully I didn't.
Focus:
Focusing was quick and quiet although it did throw a paddy a couple of times going from one end to other before it focused properly. I did end up having to watch my focus points sometimes, especially in the jousting where I quite often ended up focusing between to the crowd, this is less the lens more me and to use it though. The downside to the big'ol zoom is the fact you can only focus at 1.8m away, I got caught out a few times leaving it in 6.5m focus mode but this is by no means a macro lens.
Dust:
I did inspect the sensor after and couldn't find any dust on it but it may live up to it's 'dust pump' name over time but not for me.
IQ:
Image wise it produced some cracking photos, I have 15 billion to go through but I've uploaded three that caught my eye, only issue sometimes was the aperture fully extended is f/5.6 so even in sunny conditions I was at ISO 400 to help with shutter speed. Otherwise spot on and worthy of the L symbol.
Photos here