I didn't spend this year for Wikipedia because of the advertising. It really got on my nerves:
![Wikipedia advertising - Fundraising campaign](../images/2013/01/wikipedia-advertising-300x85.png)
But you can simply disable it:
![How to disable Wikipedia fundraiser](../images/2013/01/wikipedia-disable-fundraiser-300x153.png)
You only have to go to:
Preferences → Gadgets tab → Browsing → check "Suppress display of the fundraiser banner"
Now I'm happy ☺