I found this little bit of speculation on the Motley Fool site.
Fool.com: Google's Billion-Dollar Shopping List [Commentary] June 3, 2004: "Perhaps Tickle was Monster's most interesting acquisition"
Apparently Google's IPO may spur it to buy Monster who recently purchased Tickle in May. So say the Motley Fools.
I guess it is all about who has the eye-balls. Amazon, Ebay, Google, Monster are all recognizable to most web-surfers. Other companies like Double-Click, most gambling sites, Blind Date, Lava Life (and other various dating sites) are infamous (but still well known) sites. If the reputable companies buy up all the Tickles, hopefully the amount of spam on our favorite websites will decrease.
Or maybe it will quadruple!