When I broke another pedal on mile 25 or so of a group ride the Monday after the Almanzo 100 I knew I had to switch.
Shimano was the clear choice for me. To put it simply thee more I ride the more Shimano parts I use. The appeal of slightly flashier/lighter/cheaper/whatever equipment just no longer is there.
I had a much harder time switching to the road pedals (7900 dura ace) than I'd like to admit. Maybe I should have switched over slowly, only using them on group rides initially, but bad starts (and restarts after free laps) in the northstar crits were actually a big enough issue for me to influence the outcome of the races. I'm still not 100% proficient.
On the mtb/cx front the switch went a bit better. I went with the 540s and got them right before the week long touring trip I took to the U.P.. Initially I rode them with the tension all the way loose which I found replicated the feel of clipping into the CB pedals very well. I noticed the longer spindles, but it was never something that bothered me on that trip (60+ hours on my bike in 8 days). Anyways, after that trip I was fairly confident in being able to clip into the pedals. I still am not quite as fast as I used to be though. I think my starts suffered a little bit until well into November. Dismounts are not an "issue" but the pedals do not allow me to walk my left foot out leading into barriers as easily as with the other pedals and I've had to change my technique some. I have been pleasantly surprised by how well they work/clear mud. If anything my experience this year was that mud performance was improved vs. the crank brothers.
In the end I'm not looking back.