It's off for historical reasons i.e. the default in vs.net 2002 was option explicit on, and option strict off, so thats what the original Ibuyspy was written on, so we inherited that. By the time it would have been likely to be changes there were a huge number of modules implicitly relying on that setting, so it would be a breaking change. Also, setting option strict to on, disallows late binding which is a technique that is used from time to time (and will be more and more now that dynamic coding has become fashionable again - this is why the DLR release has languages such as iron ruby and vb.net, but not c#).

However, those points aside, from 2.0, and particularly the advent of partial classes, we can now apply differing values to differing sections of code, so perhaps it's something we should look at again (though IMO the performance benefits are miniscule , and the danger of breaking code and existing modules is a much higher risk)

Cathal