Biggest reason we use openfire is the group push and auto-join conference/bookmarks features. We started out using Jabberd2 (this is long before we started using ebox) but switched to openfire when a friend told me about it's features.
Group push auto pushes buddy lists to groups specified, which is a really nice feature for teams since when a new member is added to a team everyone automatically has them added to their buddy list.
Auto-join conferences is essential for us since conference chat is our primary method of comunication/organizing projects. It makes people join premade conference rooms specified and limits the amount of 1 on 1 chat. It also populates the chat client's (we use Spark, made by the same guys who make openfire) bookmarks with ones we specify so people have the same lists of web bookmarks and get updated auto when we need to change them.
Other features that are really usefully (not sure if they're available/will work in Jabberd2) are:
IM gateway/protocol translation, so people can register their MSN, Yahoo, Gtalk, irc, etc accounts and use them all in the same place.
SparkWeb which is a web based client people can log into and use from anywhere if they're away from their workstation.
Whiteboarding and code collaborating via plugins for the Spark client
Fast Path which allows for "tech-support" style queing for clients via a web interface
Asterisk and SIP phone integration