My first thought was to criticize Accel for such a massive distribution. Sure 50 million shares represented less than half of the VC firm’s holdings, but wouldn’t it risk depressing the company’s stock price by flooding the market with shares? And, in so doing, reduce returns for some of those limited partners who needed to sell?

But then an emailer reminded me that the capital gains tax rate is scheduled to increase on January 1, from 15% to 20% (plus a bit more, if healthcare-related taxes are included).

This is where it gets tricky. Lots of Accel’s investors are nonprofit institutions like university endowments and charitable foundations. They would prefer the higher stock price, since tax rates are irrelevant to them.

But others, like corporations and high-net-worth individuals, are subject to capital gains taxes. And put Accel’s partners into that latter category, in terms of both returns from monies invested into funds and for carried interest generated by third-party investments. For all of these folks, capital gains rates matter.

Look, I’m not arguing that Accel distributed such a large number of shares for the purpose of tax arbitrage. First, because I think proper portfolio management makes much more sense as the primary driver. Second, because it could have bled the shares out over the next couple of months, thus protecting both the stock price and the tax incentive.

But it’s worth remembering, particularly for the next lockup expiration, that certain investors will benefit from getting shares out in 2012 rather than in 2013. Including the VC firms themselves.

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