I have a Kindle 2 and using the WAP site, I logged in fine, searched for caches by zip code fine, found and logged a note on one of my caches just fine.
It wasn't a very fast endeavor, but then again, it wasn't all that slow either. I'm impressed.
I also have a Kindle2 and my experience was the same. In addition I was able to display the google map of the cache location. I was also impressed.