We're not close to reaching the block size limit
You and I have differing opinions on what "close" is then.
Here are the last 10 blocks:
214657 48.711
214656 31.016
214655 133.286
214654 261.695
214653 15.265
214652 42.617
214651 36.039
214650 204.577
214649 3.489
214648 214.828
The average for these is about 100K.
And it appears to be approaching the rate of 300 transactions per block (about 43K transactions per-day).
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http://blockchain.info/charts/n-transactions-per-block?timespan=180days&daysAverageString=7This is a transaction every two seconds.
A lot of these are microtransactions (e.g., under a dollar's worth of coins) used for wagering, so the blockchain already has a way of limiting those:
If the blocksize is more than 250 kB, transactions get increasingly more expensive as the blocksize approaches the limit of 500 kB. Sending a transaction when the blocksize is 400 kB will cost 5 times the normal amount; sending when it's 499 kB will cost 500x, etc.
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http://en.bitcoin.it/wiki/Transaction_feesBut twelve months ago no SatoshiDICE existed and nobody knows what 2013's breakaway Bitcoin success story will be but what if there are four of them, each as popular as SatoshiDICE is today. Then the blockchain size limit (at the current restrictions) will be reached.