I use google maps for about 15-20 minutes a day, every day. I didn't even realize we had been upgraded to a new version - Just took a quick peek, and the 4-5 things I do (Satellite, Transit, Traffic, Address Lookup, Driving Directions, Street View) - all seem to work pretty much the same on both maps - the newer interface seems to be more modern to me.
I have to believe, based on my what I would consider my own moderate google maps power users perspective, that fewer than 1% of google maps users will have any issues with this change.
New maps on computers without some sort of GPU acceleration is pretty painful and laggy compared to old maps. Compare maps.google.com to maps.bing.com and there is a noticeable performance difference (obviously not feature parity though).
I have to believe, based on my what I would consider my own moderate google maps power users perspective, that fewer than 1% of google maps users will have any issues with this change.