The GMail import is an interesting problem faced by almost every Social Network as they almost all now use libraries to make this easy. It’s also faced by untold numbers of Twitter utilities and many other use cases. There are two lines of attack to deal with this which are related.
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Come up with a formal API for exporting and syncing Social Graphs between Social Networks. See Brad Fitzpatrick. Then get it adopted widely.
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Come up with a formal API equivalent to OpenID to allow a user to authorise Site A to make data requests to Site B on their behalf. See oAuth.
The problem is not Facebook’s. They’re just using a common bit of code to help the user find their contacts. And it’s not GMail’s. They’re just providing a tool for a logged in user to export their contacts. Unfortunately, it’s the industry’s problem for not coming up with a secure method of doing what the user wants to do.