Thanks for your responses!
IQ is pretty much on par with the 24-105 L - quite good, very useable images. Size, weight, and handling are pretty much the same as the 100-400mm.
Hmm...that's interesting to hear. I have the 24-105L myself, used it as a walkaround at a local event last year and I'm always pleased with the quality. It's not quite on the level of the 35L or 100 macro (both are simply amazing) but it is a big step up from a P&S or the junk 18-55 that came with my old Rebel. I looked at images from the (much cheaper & lighter) 18-200 and they just weren't good enough- too soft.
There's always the issue of getting a good one versus an average one from Canon. I've got a good one.
Really? QC issues with this lens?

It's $2600 for goodness sake!! I know there's always a risk of getting a lemon with any electronic device no matter the price, but...among the working ones you'd think they'd tighten up with the premier lenses...right?
It focuses down to 2.3 feet at all focal lengths making it a near macro lens at 300mm.
wow...nice! I'm sure it's likely no substitute for a true macro lens, but still, for a lens that supposed to be able to "do it all", not bad...
1 It is one of Canon's push/pull lens designs making it a "dust pump" on the front of your camera so you need to zoom it slowly if possible.
2 It looks like a telephoto zoom even at 28mm making it hard to do any street photography with it when traveling without getting harrassed by people thinking you're zoomed in on them.
Man...the first one might kill it for me right there...I'm always VERY careful with lens changes- try to do it quickly + always indoors to minimize dust collection. After a little over a year, haven't needed to clean it or remove any large spots, although I do see small ones beginning to accumulate.
As for the second one, yeah, I never really was comfortable walking around city streets with a big white lens

...it's bad enough at events where I'm almost ALWAYS approached by someone curious or wanting pics or some other deal. To me, the 24-105L is a good middle ground- while it is bigger than the stock lenses on most DSLRs, it tends not to grab people's attention nearly as much as a white lens would, and it makes it easier to go about and do your thing.
As for the bird pic- nice shot! It does seem to be a bit soft for my personal taste though- is it straight out of camera or processed? Maybe with some DPP sharpening it would be fine. I know I have to do that to a few images taken with my other lenses too.