1) That's amazing. I'm surprised there aren't major issues, considering the differences between Androids and Black Berries.
2) I think that's cool. I have several friends with Black Berry phones who won't be able to get an Android any time soon and with this they can finally see what I'm talking about all the time!
3) Is it legal? My immediate response is yes. Android is open source, so anyone can do anything they want with it. I'm not a developer, but it would make sense that the same open source rules apply to .apk files. There could be legal issues for particular apps, like if Microsoft included a clause in their user agreement that prevented Xbox Smartglass from being run on any OS other than Android, but it would still be legal to offer users the ability to install apks, and the responsibility of each user to do so wisely. Any app that requires Google Play license check would be broken.
4) No, as Google Play, as an app market, should remain exclusive to the Android platform. Now Google apps on the other hand, those are on iOS, so why not Black Berry?