user14311: BIP 11 makes M-of-N multi-sig transactions standard --- for N <= 3. What is the current support among miners for the multi-sig transactions with N > 3? (say 3-of-6). Also, BIP 11 states: 

The current Satoshi bitcoin client does not relay or mine transactions with scriptSigs larger than 200 bytes; to accomodate 3-signature transactions, this will be increased to 500 bytes.

Does this still hold, and if yes, does this limit come into play for N > 3 or M > 3? What other obstacles are in the way of standardizing M-of-N for meaningful N?

user1307: Standard multisig outputs have max 3 keys, but it is possible to add up to 16 keys.
This limit is probably a result of the hard limit of output script size.
EDIT: source: I don't remember where I found this information. (I implemented it in Dartcoin and put that in the documentation.) As an alternative source, check out Mike Hearn's BitcoinJ implementation here.

14311: <p><a href="https://github.com/bitcoin/bips/blob/master/bip-0011.mediawiki">BIP 11</a> makes M-of-N multi-sig transactions standard --- for N &lt;= 3. What is the current support among miners for the multi-sig transactions with N > 3? (say 3-of-6). Also, BIP 11 states: </p>

<blockquote>
  <p>The current Satoshi bitcoin client does not relay or mine transactions with scriptSigs larger than 200 bytes; to accomodate 3-signature transactions, this will be increased to 500 bytes.</p>
</blockquote>

<p>Does this still hold, and if yes, does this limit come into play for N > 3 or M > 3? What other obstacles are in the way of standardizing M-of-N for meaningful N?</p>
 1307: <p>Standard multisig outputs have max 3 keys, but it is possible to add up to 16 keys.</p>

<p>This limit is probably a result of the hard limit of output script size.</p>

<p>EDIT: source: I don't remember where I found this information. (I implemented it in <a href="https://github.com/dartcoin/dartcoin-lib" rel="nofollow">Dartcoin</a> and put that in the documentation.) As an alternative source, check out Mike Hearn's BitcoinJ implementation <a href="https://code.google.com/p/bitcoinj/source/browse/core/src/main/java/com/google/bitcoin/script/ScriptBuilder.java#132" rel="nofollow">here</a>.</p>
