I was successfully using 1Password with the Mountain Lion DP4 on my mid-2011 13" MacBook Air.
After applying the update to DP4 that Apple released yesterday, Safari started crashing upon launch.
I deactivated extensions one-by-one, with 1Password being deactivated last. After deactivating 1Password, the crash-on-launch ceased.
The DP4.1 update is not affecting my iMac. The only difference I can think of is that the MacBook Air has the Power Nap feature.