Evangelize your customer base: leverage the network to spread your message, and to convert customers into advocates
Differentiate your brand: at this point, companies that blog today are the vanguard. Be forward thinking, and show your customers, your suppliers, and your competitors that you're serious about doing business the 21st century way.
How about "Increased Sales: by staying in contact with you customer base, you a) can let them know when new products/services come available, b) maintain top of mind awareness, c) build a relationship that will weather the inevitable slip ups.