user12039: I realize this question may not have an answer and therefore might not be suitable for SE, but I'm very curious about OP_RETURN transactions.
OP_RETURN transactions appear to be the accepted mechanism for inserting metadata into the Blockchain. Considering the innumerable uses for metadata (contracts, colored coins, proof of ownership...), I foresee more and more non-monetary transactions filling up the Blockchain. 
Will that be bad?

user2306: I don't think so, because the use case of, "I need to pay (the equivalent of) five dollars to buy this comedian's work is more common than the use case of "I need to store this 128-bit string for an indefinite period of time." 
Prediction: By the end of 2016, transactions intended to hold metadata instead of actually sending coins will make up less than 10% of the blockchain's size.

user12983: It is reasonable solution. The main problem is not in the size of blockcain itself. The problem is in growing the number of unspent outputs. OP_RETURN outputs do not increase size of Utxo database

12039: <p>I realize this question may not have an answer and therefore might not be suitable for SE, but I'm very curious about <code>OP_RETURN</code> transactions.</p>

<p><code>OP_RETURN</code> transactions appear to be the accepted mechanism for inserting metadata into the Blockchain. Considering the innumerable uses for metadata (<a href="https://bitcointalk.org/index.php?topic=708193.0" rel="nofollow">contracts</a>, <a href="https://en.bitcoin.it/wiki/Colored_Coins#Example_of_an_Open_Assets_OP_RETURN_marker_output" rel="nofollow">colored coins</a>, <a href="http://www.proofofexistence.com/about" rel="nofollow">proof of ownership</a>...), I foresee more and more non-monetary transactions filling up the Blockchain. </p>

<p>Will that be bad?</p>
 2306: <p>I don't think so, because the use case of, "I need to pay (the equivalent of) five dollars to buy this comedian's work is more common than the use case of "I need to store this 128-bit string for an indefinite period of time." </p>

<p>Prediction: By the end of 2016, transactions intended to hold metadata instead of actually sending coins will make up less than 10% of the blockchain's size.</p>
 12983: <p>It is reasonable solution. The main problem is not in the size of blockcain itself. The problem is in growing the number of unspent outputs. OP_RETURN outputs do not increase size of Utxo database</p>
