From the official DMB site:

Keyboardist Butch Taylor has decided to leave Dave Matthews Band. We are saddened by this sudden news but he has our full support. He’s given so much to us and our audience through the years and he will be missed.

Butch Taylor has been with the band for 10 years, and was with them everywhere they went; studio and road included. Fans always wondered why Butch was never recognized as an official member of the band, but many considered him just that. We at DMB Fan Site would like to wish Butch the best of luck in the future!

UPDATE: From sources over at antsmarching.org, it has been confirmed that Butch left on his own accord, and for “personal reasons”. Once again, best of luck!

Source: Official DMB Site