I'm developing on the Test network. Are there any "rules" or communication methods I should adopt?
Testnet code has been modified to lessen the impact of fluctuations of hashing power mining against testnet:


http://github.com/bitcoin/bitcoin/pull/686


If you wish to test against your own testnet, or think you might interfere with others needlessly, then Testnet-In-A-Box is for you.

Now this doesn't mean you shouldn't use Testnet -- especially if you find something you think might be disruptive to bitcoin.  Feel free to verify your suspicions on Testnet even if it slams it hard.  That's why it exists.