If you download blocks from a client server site like bitcoincharts instead of waiting for the bitcoin client to update through peer to peer, what exactly are the risks? Can the bitcoin client belong to a bitcoin fork and can the coins in the wallet become worthless?
This was addressed here:
How can one download the initial Blockchain data files securely?
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http://bitcoin.stackexchange.com/questions/3551The problem is that the client doesn't validate each block on startup, so unless the client downloads the blockchain from the P2P network blockchain, you are exposing yourself to the risk where you have invalid data in your data files. If a manual download was offered with the intention to defraud, this could make you vulnerable to a double spend attack against you that could be successful.
With the version 0.7 client, -loadblock= is now available and with that you can manually download the blockchain data files, but instead of using them directly you can load the blocks from the manually downloaded data files. Thus the blockchain is loaded securely and as fast as your system can go. There is no security risks as long as after the load is done you let the client finish the last bit of catching up to protect against the chance that the longest chain in the manual download had something other than the current longest bitcoin blockchain.
[Edited for readability]
