User blog comment:Emptylord/Season 3 - PBE Patch Notes/@comment-82.158.185.52-20121110135409/@comment-82.158.185.52-20121110140030

Also: Phantom Dancer now ignores unit collision.

Yeah, Phantom Dancer has had its' statistics extensively readjusted. It lost a *lot* of movement speed and a little bit of attack speed. It's also slightly cheaper and thus less slot-efficient.

It's been known for a while that Phantom Dancer was just too good but nerfing it would've caused a drastic effect on AD carry mobility / balance for a while. We've shifted some statistics around into other items that AD carries can easily fit into their builds and now PD doesn't have to be the king of both AS, Crit and MS.

On the plus side, it now has Ignore Unit Collision on it though. How useful that passive is, I'm not sure - but it is something that people have been asking for quite a while on their carries.

Source: http://na.leagueoflegends.com/board/showthread.php?p=31242476#31242476