if_igb crashes system

bringing up igb0 is currently causing my 10-CURRENT box to become very
non-responsive (as though downclocked to some 100 KHZ...very, very, very
slow).

cmdwatch 'vmstat -i' shows the interrupts get assigned for igb0, and
about 1 second later the machine is essentially non-responsive.

anyone else seeing if_igb issues suddenly?
the machine is running off a cvsup from about 75 minutes ago.

I was only able to access the system after removing interface configs
from rc.conf, which made me suspect polling initially, however even
issuing "ifconfig igb0 up" with no media causes the issue to appear.

Let me know what additional diagnostic data may help?

Matt