Gumtree is a great site, it's a sister site to Ebay and has grown a lot over the years. I definitely say try it, there's money to be made, I use it nearly as much as Craigslist now.
Gumtree still has a long way to go before it can reach CL status, but it is the biggest one in the UK i think. Nice and easy to submit your ads
Gumtree works best for the UK market and is a great source of advertising. It has gained a lot of reputation in a short period.
I've still seen nothing bad about gumtree and they are sending lots of uniques to my site - only google sends more
my friend has a new site which is similar to gumtree except it covers uk countys instead of citys town etc. http://www.tytia.co.uk incase you want to look
he had the first part made by someone on scriptlance then coded it and developed it to what it is now.
gumtree earns me more money than cl or google. being from the uk iv used it for a while. its the best classified site for uk. vivastreet.com is also quite good.
i use adoos too. only just started using them so havnt really pushed on them yet. will have to see how good it is
I have never been able to log on to pooka but I'll try the others mentioned and compare them with my inititial gumtree observations