I fail to understand why people complain about lower-quality airlines like CA being able to join Star Alliance. I mean, Star Alliance never promised anything about quality - only a huge network, as seen from their tagline "The way the earth connects" .

Honestly, being HKG based, I don't find Air China that bad - although this does depend on aircraft type - I would not want to find myself flying on one of their 744Ms from PEK to JFK. At the other end of the spectrum, their newly-delivered 77Ws are really nice, not to mention the A330s they've had for a few years now equipped with PTVs and AVOD, and most of their A321s are under 3 years old with deliveries coming every month. With Cathay's help in managing the airline and supposedly after joining Star Alliance, service has improved (particularly with English language ability on long-haul flights - it's generally ok on domestic ones), meals are so-so although this depends on taste/cultural preferences.

p.s. Air China is now one of the big decision makers within *A - so no, they won't get kicked out.