If you do, why is it? I myself have several (I count 7, actually.) I give each different purposes i.e. text chatting. However, for site where I was looking for pen pals, it turned out that I have to upgrade to send them messages. So, I also want to know some other problems if any that you've gone thru.
I have an account on italki.com, lang-8.com, and some others.
I think each resource has something different to offer. Some good, some bad.
The best resource is resourcefulness, so just draw what you can from a website or book (as long as all of the information if reliable).