In answer to Wendy's questions, I've already said quite a lot (too much?) here about why I think Twitter is great, particularly for cataloguers. I've evangelised about it to quite a few cataloguing people who have then tried it, or gone back to give it another go and seem quite happy with it now :)

It is useful for finding out news, following developments, networking, asking questions and finding out what others are doing, finding out about events and following them using hashtags.

Good accounts: obviously I'm biased so I'd recommend @HVCats and they have a list of cataloguers they maintain which is a good place to start to find like-minded people to follow:
https://twitter.com/#!/HVCats/lists
Becky Yoose @yo_bj also maintains what she calls "magical metadata fairies" (I admittedly prefer the old title of "troublesome catalogers"), which has more US-based cataloguers and is also a great place to start:
https://twitter.com/#!/yo_bj/magical-metadata-fairies-8

For training/events information, there are various CILIP and ALA accounts:
@CILIPinfo, @CILIPRareBooks, @ALA_TechSource, @ALCTS_ARC and so on

I re-tweet questions about cataloguing, information about cataloguing (especially RDA and that kind of news), information about conferences and events, things relating to coding & cataloguing and anything I think may be of interest to the cataloguers I know. I sometimes am able to put people in touch with each other if one is asking for information I know the other one has. I do a similar thing when tweeting from the High Visibility Cataloguing account, plus linking to stories about cataloguers/cataloguing departments/new initiatives and that kind of thing.

Celine