Lavasoft is currently facing the wrath of Ad-Aware users due to the fact that it removed WhenU from its definition file. A recent conversation I had with PC-Tools, maker of Spyware Doctor, gave me some insight into how this happened. Antispyware companies use a test, or matrix, to determine if software qualifies as adware. If it meets certain criteria, it's adware.
Companies like WhenU are doing everything they can to not be labeled adware. WhenU managed to change the behavior of its software just enough so that Lavasoft took it off the definitions list. I haven't looked at WhenU lately, but if it still serves pop-up ads, in my book it's still adware and Ad-Aware should remove it.