I applied for literally hundreds of jobs through Monster; never got one that way. However, twice somebody called because they’d seen my resume, and I got at least temporary work.
I have gotten several jobs through monster (including the one I have currently) and though it is a wonderful way to get your information out there it kind of limits you to customer service/temporary/retail/etc kinds of jobs. Very little else is available there. I am trying to get out of the customer service category (right now I am an insurance agent but I do mostly customer service things for my company because of my work history) but I have been doing it for years and I have no idea where to look for other things. I am on linkedin as well and just kind of watching and waiting for the perfect job to come along. I might be waiting for a while! 
My company uses Monster, far better value than the ads we have taken out in the newspaper and better/cheaper than using headhunters.
Last time I was looking for a job (a whopping 5 years ago), I had some luck getting leads through Monster and Workopolis.
Mind you, these were mostly ads that had been placed by recruiting agencies and headhunters, which placed generic “bilingual call centre rep needed” type ads. There’s a big need for qualified reps who are fluent in both official languages, especially with the high turnover in the call centre world, so there’s definitely no shortage of positions. I found a contract FT position with one large telecom via the first agency, and then went on to find a permanent FT position with another large telecom shortly after. So I guess Monster was actually pretty good to me, all things considered.
Next time around, I’ll probably skip the middleman and go straight to well… ummm… the other middleman (ie. a reputable headhunter).
I got my current job on Monster.com, and it’s fantastic. I’d recommend a more specialized site for your trade if it’s available, but for me (switching job types) it worked out pretty well.