Brandon Bailey of The San Jose Mercury News covered the Tumblr Yahoo! deal and reached out to Brian Solis for his thoughts. Following is an excerpt… Many adults already use multiple services for different purposes, such as Facebook for friends, Twitter to follow celebrities and LinkedIn for professional contacts, said Brian Solis, principal analyst at Altimeter Group. But when there are so many alternatives, he added, “Facebook is going to have to compete every day for our attention.” “We will…