Leonard's mother (Christine Baranski) comes to visit, much to his dismay. With her degrees in psychology and neuroscience, she soon makes Penny, Howard, and Raj question themselves. As one might expect, Sheldon finds her fascinating. To relieve the tension, Penny and Leonard drink together, which leads to making out, which almost leads to sex.
Like any fan of the show, I want to see Penny and Leonard end up together. They could have "done it" last night, but if they had, Penny's relationship (general dynamic) with Leonard would resemble many of her previous flings, and they both deserve better. So I expected Leonard's mother to walk in on them. That didn't happen, but Leonard did bring up his mother at a crucial moment, and Penny threw him out of the apartment.
Early in Season 1, Leonard may have just wanted to bed Penny. I like to think that's changed, but sometimes I'm not sure it has. On the other hand, Penny wanted to talk with him the next morning, and they showed a silent understanding, suggesting they want more than sex from each other.
I don't speak with much authority here. My most serious relationships consist of me being serious about someone, and the someones turning down dates (or in one case, announcing her engagement right before I would've asked her out). Once upon a time, though, someone I was serious about was drinking to get over being stood up by the object of her affection, and she invited me to drink with her.
I was of age, and always imagined I'd drink in this sort of situation, because we'd love each other and it would be okay to let my guard down, give up some control. But when it came down to it, I passed. Actually, I doubt even drink would've made her see me as I wanted. But maybe if I'd drunk with her that night, we'd be closer friends, I'd understand her better.
Anyway, I'd like Leonard and Penny to go into it with their eyes open, appreciating quirks they bring out in each other.