I too think they're a good idea, and would go for one if I hadn't already taken a year out. I know its a bit silly, but I feel like I'll have wasted more of my life if I now take up a 4-year course as opposed to 3.
However, if I wasn't in this position I'd strongly consider it, particularly at somewhere like Surrey as I'm interested in Counselling Psych, and they could set you up on a fantastic placement for it with their departmental connections.
It's definitely a huge advantage to get yourself free work experience - but I think the placement courses are obviously better for those absolutely sure they want to continue with Psychology at a postgraduate level. If one was unsure then they should probably go for a straight 3-year honours. Its a course for the committed I think.