This site originally started as stamps only. Then it branched off into coins... then ultimately having a goal to branch off into more collectibles, including comics, die cast, sports cars, and just about anything you can think of. Postcards in particular are doing well. It is still a "young" site, but a lot of people are finding it to be a great alternative to the big boy, if you know who I'm talking about.
The moderators here are very responsive and fair, so you can still actually get some personal attention. Traffic is light (compared to the big boy), but it is getting better and better. It really is what you make of it, and it seems to be trending in the direction of goodness. But don't expect outstanding results immediately, unless you are REALLY skilled and bring a huge customer base over, or really really lucky. Patience, and hard work to get noticed are the key.
Although there are always some features one wishes worked a little differently, I think you will find the site really darn cool with some of the things it can do (many of which were suggested by the membership). Stick around, don't be a stranger in the forums (in fact, it's another way to get noticed), and enjoy it!