The meteor plot (as first seen in the film Meteor in 1979) isn't exactly new,
Even older than that--L&C stole from their own past, there is an episode with the same plot as "All Shook Up" in the old Superman TV show from the 50s with George Reeve. (Sadly enough, growing up I saw more of that show on Nick at Nite than I did of L&C when it originally aired.)
The weirdest was seeing First officers Will Riker and Chakotay in episodes of L&C. Especially since Chakotay looks a lot older in the L&C episode "Fly Hard" than he does three or so years later when Voyager first aired.
Although, I would have to say the absolute funniest time I have seen an actor in a different TV show was an episode I watched from the first season (or maybe it was second season...) of NCIS--Adam Baldwin plays a Marine commander and the only other thing I have ever seen Adam Baldwin in is Firefly/Serenity and his character Jayne Cobb is *totally* not a Marine or anything close...except he likes guns...big ones...
