It really...REALLY irritates me when a wrestler joins a new promotion and is given a new, worse ring name.
I understand WHY it's done. Obviously Vince wants to own the trademark for the ring name of his talent, but it still annoys me. It rarely used to be the case, as during the Attitude era we saw talent switch sides on a regular basis with ring names USUALLY staying the same.
Pretty much all of the ECW talent kept their ring names after joining the WWE, same with guys like Dean Malenko, Chris Jericho etc, and the name changes usually occured due to gimmick changes, that was all.
It irritates me when guys like Tyler Black sign with the 'E and are given a crap ring name like "Seth Rollins", or Mistico had to change his ring name to "Sin Cara". It's worse in TNA, when former WWE guys come in and have to use alternative names as WWE own the trademarks. For example, when Billy Gunn arrived there he was "The Outlaw", The Dudleys had to become Team 3D, Test became Andrew "The Punisher" Martin, and so on and so on.
The ring name of a wrestler does not affect how entertaining they are in the ring, but I have just always preferred seeing a guy I know by a certain name show up unnannounced, and the commentators screaming "Oh My God, XXXX is here", with the fans knowing who it is, and them using their recognised names. For example, Chris Jericho's debut was awesome when "JERICHO" appeared on the titantron, and the crowd went crazy.
Other cool examples of wrestlers debuting using their famous ring names in WWE were Booker T, Scott Steiner, DDP, Goldberg and the nWo.