I uploaded a redesign of m0mchil's getwork to SVN rev 189 (version 31601)

m0mchil's external bitcoin miner idea has solved a lot of problems.  GPU programming is immature and hard to compile, and I didn't want to add additional dependencies to the build.  getwork allows these problems to be solved separately, with different programs for different hardware and OSes.  It's also convenient that server farms can run a single Bitcoin node and the rest only run getwork clients.

The interface has a few changes:

getwork [data]
If [data] is not specified, returns formatted hash data to work on:
  "midstate" : precomputed hash state after hashing the first half of the data
  "data" : block data
  "hash1" : formatted hash buffer for second hash
  "target" : little endian hash target
If [data] is specified, tries to solve the block and returns true if it was successful.  [data] is the same 128 byte block data that was returned in the "data" field, but with the nonce changed.

Notes:
- It does not return work when you submit a possible hit, only when called without parameter.
- The block field has been separated into data and hash1.
- data is 128 bytes, which includes the first half that's already hashed by midstate.
- hash1 is always the same, but included for convenience.
- Logging of "ThreadRPCServer method=getwork" is disabled, it would be too much junk in the log.

ribuck's description is spot on.

Pool operators can modify their getwork to take one additional parameter, the address to send your share to.

The easy way for the pool operator would be to wait until the next block is found and divy it up proportionally as:
user's near-hits/total near-hits from everyone

That would be easier and safer to start up.  It also has the advantage that multiple hits from the same user can be combined into one transaction.  A lot of your hits will usually be from the same people.

The instant gratification way would be to pay a fixed amount for each near-hit immediately, and the operator takes the risk from randomness of having more or less near-hits before a block is found.

Either way, the user who submits the hit that solves the block should get an extra amount off the top, like 10 BTC.

New users wouldn't really even need the Bitcoin software.  They could download a miner, create an account on mtgox or mybitcoin, enter their deposit address into the miner and point it at anyone's pool server.  When the miner says it found something, a while later a few coins show up in their account.

Miner writers better make sure they never false-positive near-hits.  Users will depend on that to check if the pool operator is cheating them.  If the miner wrongly says it found something, users will look in their account, not find anything, and get mad at the pool operator.