Have used the 100/2 and 50/2. They are superb, noticeably better than anything Nikon has in the same focal lengths. The other real gems seem to be the 21/2.8 and 135/2. From what I've heard/read, the 50/1.4 and 85/1.4 are not such a big leap over the Nikkor equivalents. But the wide angles and makro-planars are definitely seriously good (and expensive).