I have more jabber accounts than an average guy has an e-mail address. As Jabber usage will start to grow, and different communities and organizations will adopt Jabber as their choice of communication technology (rather than today's e-mail, or e-mail-like systems found in forums and social network sites), we'll have to find a way to connect jabber accounts of a person into one (or a few) bundles.
Of course, there exist approaches like Psi's multiple account system, as well as using Gaim, or other MPIM for jabber purposes, but none of them is a real, protocol-level solution.
But we can do this by Jabber-To-Jabber transports, like j2j does.
It's a XEP-0114 compatible jabber component, so it's suitable for most jabber servers.
I was constantly asked for this feature, mostly to connect gmail accounts into a new system, so here it is. Thx for Steve for recommending.