The concept of tax loss selling is not new – if you are sitting on unrealized losses in your portfolio, you liquidate those investments before year-end so that way you can crystallize the capital loss. The capital loss can be offset against capital gains of up to three years prior (e.g. a 2010 loss can be applied to 2007, 2008 or 2009 gains). If you think the investment still has merit, then it can be repurchased 31 days after the sale to avoid the “wash sale” rule (which would defer the loss and bake it into the cost basis of the new purchase).
As such, a common tactic is to look for securities that have not fared well during the year and purchase them close to year-end as there is likely to be more supply pressure.
It is also possible that this year there will be supply pressure on the income trusts that will be converting to corporations on January 1, 2011. As it is financially optimal for Canadians to be transferring these securities outside of registered accounts and into non-registered accounts, it will not be surprising to see some anomalous price action as the year comes to a close. Even though assets can be transferred between non-registered and registered accounts (by doing an equal-value asset swap in an RRSP, but not TFSA) there is likely to be extra volume seen on the exchanges.