Networking with other library people can be useful. It can give you an opportunity to share what you know (I don't know much) and get some info and ideas from them too.
I have been to a couple of library networking days where there are presentations and 'workshop' sessions, where you can choose which group you would like to do which is more relevant to your job. Not sure about there being another one of these as last year's was cancelled because of lack of attendance. Reason being their Trusts wouldn't pay the travel fairs.. but cutbacks are another story...
The other networking I did was the NVQ. There were monthly sessions where candidates could meet up and work and have opportunity to talk to their fellow candidates and their assessors.
As for online networking sites, I hadn't joined any except for the LISMED and JSCMAIL mailing lists. On recommendation on the CPD23 I joined the LISNPN. It says New Professional which I'm not but I thought there may be some library assistants on there.
I set up a Twitter and Pushnote account, which I don't think I will be doing a lot with especially Pushnote, which is largely a waste of time and will be deleting my account soon. I'll give Twitter another chance, I may have to follow more relevant people. Also I will have to follow more of the blogs.