It seems transition effect for zooming in OpenLayers does not work in IE7. I checked some of the development examples (for example this one) with IE7 and they show no zooming effects. Did I miss something?
Its the animated zooming that doesn't work, not the Transition effect (transition effect is the 'temporary blurring' of the layer before the tiles of the next zoom level load). I imagine this is just a limitation of Internet Explorer 7. Especially since the dev examples don't do it either. I am fairly sure that it does this effect using transform css properties, which are not avilable in IE7.
However, whilst writing this I came across this GitHub pull request which has a link to an example map with animated zooming working in IE7 (albeit no where near as slick). So it does appear to work somehow in IE7 in that example. Sadly my lack of knowledge of how GitHub works means I don't understand if the code written for that pull request actually got merged into the master.
In my opinion I think as long as your animated zooming works in most browsers, having IE7 fallback to working the old way is not a problem, might even convince a few people to upgrade their damn browsers!