Opera's BitTorrent implementation is never meant to replace external clients for people that use BitTorrent a lot. Our goal has always been to have an easily accessable and workable client for casual users of BitTorrent, eg. for downloading linux distributions, game trailers, etc.
In this post, I will talk a little bit about the addition of Peer Exchange support in the BitTorrent client. The changelog says "Added support for the BitTorrent peer exchange protocol, which is compatible with libtorrent and µTorrent".
The implementation in Opera is encapsulated into a extension protocol for BitTorrent, namely the one described in the extension protocol specification. The extension supported is "ut_pex" which is the peer exchange message sent by µTorrent, all clients based on libtorrent, KTorrent and many other clients. Azureus is using a different and incompatible message for peer exchange, so Opera 9.5 Alpha will not exchange any peers with this client.
The extension protocol seems to be the only relatively well designed solution for extending the protocol, and several clients already support this protocol and some of the extensions encapsulated in it.
Further improvements to the BitTorrent support is planned for Opera 9.5 final.