The conductor Michael Tilson Thomas is approaching both his 20th anniversary as music director of the San Francisco Symphony, and this December, his 70th birthday. Seemingly as dynamic and tireless as ever, he brings the orchestra to Carnegie Hall for two programs. On Wednesday this acclaimed conductor of Mahler will lead the composer's Seventh Symphony. His recording with the San Francisco Symphony won two Grammy Awards in 2006. On Thursday, he conducts the New York premiere of a Samuel Adams piece, Prokofiev's Second Violin Concerto (with Gil Shaham), and Ravel's complete "Daphnis et Chlo�," joined by the New York Choral Artists.