Working happy and with humour == working better
I've only been working for near 6 years, but I've been in 4 different companies and lots of customers, so I've "tasted" very heterogeneous "work ecosystems".
I love my work, and I enjoy a lot developing, so whenever I can, I try to add a humour component to my daily work in order to make it even more enjoyable.
This is specially useful when you have tedious tasks, or a tight schedule, or you enter in a crunch-time phase. I've worked with teams in a "hostile environment" and the results were clearly worse than in happy, nice ones.
Now that at ilitia we've got a "Windows Live Team" (small one but I hope to have it increased soon), I try to keep it "in good shape" by making all sort of jokes and encouraging my pals to do the same.
A good thing is that working developing Windows Live Agents is fun "by itself": When your agent doesn't works is not like getting an exception in .NET and your application crashing. Your agent may "be shy" (not respond to something expected), may be "drunk" or "lost" (answering wrong things) or it may even "come alive" (when does something really unexpected :)
Also, we sometimes like to play painting images and creating fake logos to have some fun. Here there are a few ones:
Living the Enjuto Mojamuto way of life!
Our "Windows Live Team" unofficial signature logo :)
The A-Team "mashup" (in Spanish)
So, if you don't already do it, try to add humour to your work and you will notice the advantages ;)
Work happy, work better!