I'm starting this thread to brainstorm rule changes for -testnet and talk about a possible testnet reset for the next release.
The testnet isn't currently usable, because hashing power on it is unpredictable. Difficulty shoots up because somebody decides to throw lots of machines at it, then they leave and it takes MONTHS for difficulty to drift back down.
Here's a shot at hair-brained rules for the testnet:
+ Fix the difficulty at 1.0, no matter how many people are mining.
+ Clients reject new blocks with timestamps more than 1 minute different from their time (implies: you have to have an accurate system clock to play with the other nodes on the testnet, otherwise you'll be on your own fork).
+ Clients reject new blocks if their timestamp is less than 2 minutes after the previous best-block's timestamp.
+ Clients prefer to build on blocks that include more memory-pool transactions, instead of taking first-block-they-receive.
Goals behind those rules:
Always easy to mine
Limit block-chain growth (max 1 new block every 2 minutes)
So: could a griefer make life miserable for the rest of us under those rules? What would happen if there were five or six people with a fair bit of hashing power all trying to mine as fast as possible on testnet? (lots of block chain splits, I think, but that's probably just fine on testnet)