Don't forget that for each forum, and for each sub-forum, there are two feeds.
Example: <
http://n2.nabble.com/atom/ForumFeeds.jtp?forum=3354548>
Any reader of your
Sun News messages feed can see each new message almost immediately after it is posted.
Personally, I hate forums that require or expect me to use in-page instant messaging as a substitute for e-mail.
If I forget or do not bother to check my e-mail, that's my choice. When I make that choice, I don't want forum/service administrators to disrespect my choice by pushing things at me in some other way.
When I do not sign in to my (live) instant messaging software (there are many, many clients; and many, many services), that's my choice. When I make that choice, I don't want anyone to disrespect that by imagining ever more, and more, and more ways of pushing things to me in real time.
There are a plethora of systems and services that handle instant messaging and/or feeds, most of which are wholly complementary to the feature set of Nabble.