I haven't kept up with the coinjoin thread, but ... assuming people could trust either one individual or one entity or even 2-of-3 multisignature addresses, can a bunch of people just send coins to that one person, and he sends it to himself (consolidating all the unspent inputs into 1 output), then send them all back out to the same bunch of people (at different addresses), and this is effectively mixed?

Let me rephrase that in steps:
1. many people send coins to, for example you, 1GMaxweLLbo8mdXvnnC19Wt2wigiYUKgEB, wait 6 confirmations.
2. you then use some form of raw transaction or coin-control to get all the unspent inputs, then spend them all back to 1GMaxweLLbo8mdXvnnC19Wt2wigiYUKgEB, wait another 6 confirmations.
3. then you send the coins back to their original owners.

Of course, this method is flawed in that they (the people) have to trust you. But a service could do this and charge 1% or something, like blockchain or bitcoin fog used to (they really did mixing by not connecting users to each other.)