You see a lot of w and ww and even www in Twitter and casual chat. What does it mean? I've always thought it was わいわい but never found out. How is it pronounced?
Here's an example from Twitter
As the others have said, the "w" stands for 笑う(わらう).
You might also see someone write "ちょwww" online. This is similar to somebody saying "ちょ~かわいい" if you've seen that line before. In this case, the ちょ is actually 超(ちょう) so "ちょwww" would translate into something like "so funny" or "very funny" compared to the standard "www" or "wwwwwwwww (ad infinitum)" which would just be "lol" and "roflmao".