wide angle focus questions

I'm comparing the 16-35 2.8L and 17-40 4L for a 30D. I've read the various comparisons and reviews of both, but still have some unanswered questions:

1) Does the focusing method on both of them allow for autofocus and slight manual focus without switching out of AF mode/damaging the focus?

2) Are both weather sealed?

3) I know that the 16-35 is a bit older than the 17-40. What kind of changes (small tweaks) can I expect Canon to have made between when it was first released and now?

Thanks,
Vaughn