As for SA, I'd say my 10 dollars was well spent. It's more than a posting forum to me. There are a gazillion boards, and honestly, I mostly lurk and post in movie/tv/music/gaming/politics threads. I post in maybe 10 threads total.
But I mostly lurk.
You can spend an entire day learning something new on Something Awful. Unlike boards like GAF, which are self contained and exclusive, SA is a pretty inclusive board. Communities are formed not only within forums and sub-forums but also within whole threads. Some people only POST in one thread because the thread is so big and so many people post in that thread. The forum is just informative.
You have the ask/tell board, where you can ask a question or tell people about something. You can learn all sort of shit in this board:
Ask/Tell:

Ask/Tell (sub-forum: Tourism):

Ask/Tell (sub-forum: Business/Careers/Finance):

Like guns?
The Firing Range:

Post Your Favorite board is great for finding new shit.
PYF (Post Your Favorite):

Like cooking? Great for new recipes and local dining.
Goons With Spoons:

Like online shopping?
SA-Mart:

I can find anything, on any topic, with any opinion on this board. This is without bringing in the art, comics, movie, tv, gaming, and music forums. I'm going to be using the tourism board for planning my vacation this summer, in fact. Good resource. While other forums would dedicate something to just one thread, on SA, you will most likely have a whole BOARD dedicated to that one subject. This makes it amazing for information. I have found so much new cooking recipes, music, movies, tv, and all around interesting stuff thanks to this forum that it's ridiculous.
10 bucks well spent. There's this one thread about debt/debt collectors that is helping me SO FUCKING MUCH.