Arbitrage adds liquidity to markets.
it helps markets to become efficient.

BitFunder, BTC.TC, Litecoin Global ... should share a list of assets and their belongship into a kind of blockchain.

see
http://erratasec.blogspot.fr/2013/05/bitcoin-is-public-ledger.html
http://www.proofofexistence.com/

so it could help to move assets (shares, bonds, ...) from a place to an other one

This academic paper is interesting:

Jeremy Clark and Aleksander Essex. CommitCoin: Commitments with Temporal Dispute Resolution using Bitcoin (Short Paper). Proceedings of the 16th Conference on Financial Cryptography and Data Security (FC 2012), 2012.

see
https://bitcointalk.org/index.php?topic=28811.10