Bitcoin lead developer Gavin Andresen has made a post on BitcoinTalk to bring users attention that the threshold of blocks that are version 2 and comply with BIP 34 is about to be reached and version 1 blocks could soon be considered invalid and orphaned from the chain.
BIP 34 was accepted into the official bitcoin client close to a year ago last July in order to further standardise the process under which block creation rules were updated and has been sitting dormant until 75% of the blocks created were compliant with the new version 2 standard. Once the 75% threshold is reached then additional checks went into place to ensure that the blocks were indeed version 2 compliment.
According to recent data, of the last 1,000 blocks 821 were version 2 compliant with BIP 34 so the next threshold of 95%, or 950 blocks in 1,000 is imminent.
Under the draft, and the rules already in the bitcoin client once the 95% threshold is reached it hits the point of no return and from that point on 100% of the blocks created must comply with BIP 34 or be rejected as orphans causing a soft fork.
All previous versions of bitcoind have had the BIP 34 changes back ported to them so as long as you have updated since the middle of last year you should be safe, just to be sure though, you may wish to go to http://bitcoin.org/ and download the latest version of 0.8.1 released today.
I have included Gavin's post on BitcoinTalk below;-
Last July, BIP 34 was accepted. It specifies a "soft fork":
If 950 of the last 1,000 blocks are version 2 or greater, reject all version 1 blocks
We are getting close to that threshold: 821 out of the latest 1000 blocks were version 2.
If you are mining in a pool: there is a list of pools and what versions they are producing here. If your pool is producting version=1 blocks, you should urge your pool operator to upgrade or patch.
If you are mining with p2pool or solo and using a very old version of bitcoind: you should upgrade, or you risk your blocks getting orphaned.Gavin Andresen - Bitcoin lead developer