There are many good reasons to be involved in Wikipedia:
- It's fun.
- It's easy.
- It's educational.
- It's social.
- You can correct other people on the spot without asking their permission!
- It's exciting. Wikipedia has created literally thousands of articles in the mere months since its inception--over 2,000 per month, in fact.
- It's interesting to share your knowledge with other people, particularly knowing that others can instantly edit or react to what you've written.
See also why Wikipedia is so great.