[thedoc (OP)]

Changes in the gulf stream over the last 5000 years are destabilising trapped methane over at least 10,000 square kilometres of the US eastern margin, and if this were to be released it could cause abrupt climate changes.

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[CliffordK]

and predictions are that it could take as much as 5000 years for this methane to escape into the atmosphere.

The half life of methane in the atmosphere is about 7-10 years.

So, if the methyl hydrates are released into the atmosphere slowly, then it may be seen as an increase in atmospheric carbon dioxide, rather than a bolus of methane which may have less of an impact on the future environment.

Still, it is important to understand methane deposits, especially in "vulnerable" areas both in permafrost and shallow ocean waters.

[evan_au]

It may be desirable to mine it, if it can be done in a stable manner. http://en.wikipedia.org/wiki/Methane_clathrate#Continental
This could produce energy for consumers, and CO₂ is a less potent greenhouse gas than methane.

On the pessimistic side, if a clathrate deposit became unstable, it could:

• produce a burp of methane that could swallow a drilling rig
• or trigger a turbidity current on the continental shelf. It has been suggested that if a turbidity current accelerates down the continental shelf at a similar rate to the velocity of a tsunami (which are faster in deeper water), this can couple considerable amounts of energy into the tsunami.

[Mazurka]

The PETM is a fascinating episode as (I think) it is the only warming event where increase in CO2 levels preceded rising temperatures. 

This is important as other warming events - attributable to milankovitch cycles - rise in temperature preceded rising CO2 levels.  This relationship is often cited by those that do not accept anthropogenic climate change as an "inconvienient truth" in (the political) arguments about the need to cut CO2 emissions etc.