AutoFixture 1.0 doesn't support any sort of criterion-based selection, and in general it (unfortunately) doesn't support open generics. However, we
are tracking this issue, so if you think it's important then consider voting for it:
AutoFixture 2.0 will have a much more open extensible kernel, so it will allow you to write your own builder that contains special logic for IEnumerable<>, if you would like.
Until then, you may want to take a look at this related [discussion:205101] for hints on how you can currently address this issue.
Another couple of points worth noticing:
As a general rule, the Framework Design Guidelines strongly discourages writable collection properties, so in any case you should consider making your Shares, SharedFiles and SharedFolders properties read-only. It will also remove any need for explicitly
opting out of those properties.
You can also create a general customization of the Contact type:
fixture.Customize<Contact>(ob => ob
.Without(c => c.Creator)
.Without(c => c.Shares)
.Without(c => c.SharedFiles)
.Without(c => c.SharedFolders));
Another alternative is to opt out of Auto-Properties all together and opt in on those properties you want populated, but that's a bit less refactoring-safe, since you might later add more properties to the type, and these will not be filled out in that case:
fixture.Customize<Contact>(ob => ob.OmitAutoProperties().With(c => c.EmailAddress).With(c => c.FirstName).With(c => c.LastName));
However, the best option altogether may to enable the Fixture to create those types (such as the User type).
Please don't hesitate to write if you have further questions.