I am using it as my primary Kannada IME and it is pretty impressive. I was using the Baraha IME for Kannada transliteration until now. It is too early to comment on how Google Kannada IME handles the esoteric characters or words of the language or on its performance. But, it is definitely a good user experience, right out of the door. Google Pinyin IME has been available for years now and is a big hit. Surely their experience in that has served them well for other (easier) languages. (A Chinese language IME is any day far harder than any of the Indian languages.)
One major plus with the Google IME is that it shows word suggestions as you type. It also looks like Google IME maintains a user cache where I assume it will store the user picks of words. That should help the IME suggestions get better with time. Also to be noted is that this is yet another area where Google has squarely beaten Microsoft. All the NT flavours of Windows have always had complete Unicode support from the kernel up, but their Kannada IME was never a good experience. They stagnated development on their IMEs and look who got their goat! All in all, Google IME is a refreshing new experience to type in ಕನ್ನಡ (Kannada)!