Famed corporate raider Carl Icahn is taking his agitating to Tumblr, from now on posting his musings in the realm of cat GIFs, teenage fan fiction and some questionable respect for intellectual property. According to a statement from his namesake company, Icahn will use the microblogging platform "to communicate with the public about our company and other issues," all at CarlIcahn.Tumblr.com. So far, Icahn's sole posting is his open letter to Apple ($AAPL) CEO Tim Cook, in which he suggests that the company's shares are undervalued and that it should mount a buyback. Icahn's embrace of Tumblr comes after forays into Twitter and Facebook, plus the launch of ShareholdersSquareTable.com, a site whose splash page features an exhaustively labeled illustration of greedy corporate managers filching plebeian investors. His interest in Tumblr is perhaps a coup for Yahoo! ($YHOO), which paid about $1.1 billion for the network last year. More