Pets are becoming account wide to facilitate the abomination that has been labelled
Wowkemon around the community. But that aside the benefits of account-wide pets is bitter sweet sure it will save us all buying a pet multiple times and enabling us to use hard to acquire pets on our alts. The flip-side is that as an auction house player I'll have less opportunity to sell pets to other players in numbers. However, there are rumours of being able to sell battle pets and that may well be a better income stream than traditional pet sales anyway.
However the kicker are account-wide achievements. This for me is sweet and will allow me to recover my long lost TBC raiding achievements from when
Evlyxx was an alt to my other priest purely because he was a tailor, in particular the
Champion of the Naaru and
Hand of A'dal titles.