I've got a theory...
Hmm my theory concerning the episode swap : in this week's episode L/P were still all couply and googly-eyed (eww)...in the upcoming ep however we know from the spoilers we read, that Leonard isn't going to fit in with Penny's friends at all and basically end up drunk and all...My guess is that the writers are preparing us for the long awaited breakup!!! (I hope). I like to believe that things will go from bad to worse for L/P from this episode on! We know about the episode where they will fight A LOT (then make up again but not a problem...its the beginning of the end)...I'm hopeful!!!
Maybe after the L/P breakup...things will be awkward for them for a little while so Leonard will hang out with Raj/Howard more and Penny will hang out with Sheldob (who's still 'mad' at Leonard for the Arctic data tempering) From there the S/P friendship will grow more and more until the end of the season, where Sheldon will do something amazingly nice for Penny and they'll acknowledge that they are best friends! Then S4, these guys will be bffs! With Sheldon getting to acknowledge just how important Penny is to him! And maybe, maybe S5 we can have Penny realize that she more than likes Sheldon!
You know...realize that he's hot etc. Maybe we can have Sheldon finally date a girl from the university who isn't going to go all Ramona on him and have Penny be jealous and all...<3
OMG how I would love it if everything I wrote was to happen!!! Imagine how great it would be!!! *sigh*