One well-known example would be the Cosmic Microwave Background, which was (and still can be) observed (but not created in the lab) and which is considered evidence which confirms the Big Bang theory. This "mere observation" was regarded as sufficiently persuasive that it plunged the Steady State theory into oblivion.
Another example would be the "mere observation" of the shifting of the apparent positions of the stars near the sun during a total eclipse, which was (and is) regarded as confirmation of Einstein's theory. So far, it hasn't been re-created in the lab, so I guess the "creation science" crowd doesn't accept it.
Observations are very valid forums of supporting evidence - all I am saying is observation does not equal experimentation.