I worked for an IT Recruitment Company for over a year and I disagree with JohnMason, maybe the company he interviewed with didn't have a good rep, but generally that is not the case. In fact, it is against the law to advertise or recruit for a role that is 'non existent'.
From working in recruitment, i would definitely recommend using an agency - my only word of advice is to NOT put your CV on the likes of 'Monster' or 'Jobserve' as EVERY agency, whether they are reputable or not, has access to it and will bombard you with job roles that are 'ideal' for you!! You find the companies you want to represent you, maybe a recommendation through a friend. Also a lot of agencies have a 'recommend a friend' scheme, where if they place a friend you recommended - you receive a % of the fee!!
As jamesb said, you will probably end up on a better salary and stronger package when leaving it up to an agency, as that is there job. They do it all day every day and the more money they get for you - the more money they get themselves!!
So yes, i would definitely use agencies to find a new job!!

P.S - I can pass on details of a fantastic company (who i used to work for!!) if anyone is looking!!
