The first melody that Sheldon tries to play on his theremin after saying how much he loved the use of this instrument in the opening tune of Star Trek (1966) is, in fact, said opening tune. It should be noted though that the theremin wasn't actually used in it; what sounds like a theremin was actually a soprano vocalizing.
Penny comes up with the idea of an app that would allow people to take a photo of a pair of shoes and the app would identify them. Sheldon ridicules the idea. In 2022 (15 years after this episode aired), "Google Lens" will do exactly that.
With the exception of background extras, this episode contains no guest actors. While Howard does speak to his mother on the phone at the beginning of the episode (a scene removed for syndicated reruns), Carol Ann Susi's voice is not present, as the audience only hears the conversation from Howard's end.