I had to put that in the title so I wouldn't ruin anything for those who don't like spoilers, but it isn't actually a spoiler.
It's just that B is dressed EXACTLY the same when she's looking for Georgina in episode 1x17 (therefore, in the eyesex scene with Chuck) and when she wakes up next to him, so that will happen in the very beggining of the episode 1x18.
Here so you check:
Chuck&Blair waking up together in episode 1x18.
Chuck&Blair eyesex scene.
I'm sorry if all you guys had already noticed this... But I wanted to share it. LOL