MSDN subscriptions are per user rather than per device so as long as you’re the only person using them I think you should be free to use them at home. I’m not aware of any differentiation being applied to the workplace, unless of course your workplace itself lays down such a rule.
From http://msdn.microsoft.com/en-gb/subscriptions/aa948867.aspx:
MSDN Subscriptions are licensed to
individuals who may install the
provided software without restriction.
Software provided through MSDN
Subscriptions is licensed for design,
development, test and demonstration of
your applications.
See also http://msdn.microsoft.com/en-gb/subscriptions/aa948864.aspx.