Watch out, Yahoo, Tumblr has a history of changing its mind suddenly (R.I.P., Storyboard). Yahoo is apparently in talks to buy Tumblr, the New York–based blogging site, according to All Things D on Thursday night. If the reports are true, it would certainly fit into Yahoo CFO Chris Goldman’s recent comments that Yahoo needs to become “cool again.” It will certainly be expensive for Yahoo: Tumblr is reportedly stepping up efforts to raise the company’s valuation to $1 billion. The latest estimations put Tumblr’s value near $800 million. Representatives from Yahoo and Tumblr have not yet commented.