This is one of the few times that Leonard's work comes up and Sheldon doesn't make a derogatory comment about it. Of course, the fact that Stephen Hawking was impressed with Leonard's work and that Sheldon almost worships Hawking has a lot to do with it.
When Sheldon clinks on his glass and says "B-flat for those who don't have perfect pitch", the note produced by him clinking on his glass is indeed a B-flat.
The only episode in the whole series where something besides the end music plays over the end credits. (Raj's incessant talking to the girls from the final scene continues.)
Apparently, the dead goldfish found by Sheldon in Penny's closet in The Closet Reconfiguration (2013) belonged to Leonard, but Penny didn't take proper care of it.