In the IT industry a lot of jobs are never advertised, positions being filled by word of mouth, so it you are looking it's worth doing the networking thing and saying so to friends and colleagues and posting something in cam.misc so people are aware that you're looking. Putting your CV on the web in an open format like HTML or PDF so you can include the URL in your posting could also pay dividends. (Posting the CV as an attachment will not make you popular - see Can I post adverts in cam.*?)
The university have a page where jobs related to the university are posted and also has links to other useful places to look for jobs. Patrick notes that “it worth mentioning that it's worth checking at least one and possibly two weeks back issues as they often have jobs with closing dates that are still open that haven't got re-listed in the current one.”.
The Cambridge (UK) Web Guide has a page of links to job opportunity pages on company websites.
For IT you can find out what skills are in demand by looking at this web site.