Having marathoned the first seven episodes of this series last night, I just watched the eighth which premiered not too long ago, and thought I'd give my thoughts on the series thus far.
Brief Summary
Mysterious Girlfriend X, based on a Manga series of the same name (surprise, surprise) follows high school student Akira Tsubaki, who after tasting class mate Mikoto Urabe's drool that she had left on the desk falls in love with her. Mikoto Urabe, who is aware of the effect drool can have on people who are extremely close, realizes her and Tsubaki are meant to be together and agrees to go out with him. The series then follows their relationship and its evolution.
Although it may sound a little bizarre because of the whole drool thing, the series is so well done that you hardly notice or even think about how weird it is. Being relationship centric there is little to no fighting in the series, but the characters are all so interesting - especially Urabe - that it's never boring. There is also a great deal of comedy and the series has actually made me laugh out loud a couple of times. The main pro though is the relationship between Tsubaki and Urabe, which is so well written and orchestrated that even if no words are said there's still something interesting going on.
Cons
The only real con is that since the series only focuses on four characters extensively, it can get a little stale. But even then, the four characters that get the spotlight are so interesting you don't really notice. It could also be said that the actual romance is a little slow paced, for example eight episodes have already aired and Urabe and Tsubaki haven't kissed yet.
Bottom Line
Unless you have an erational fear of drool, or need action in your animes, Mysterious Girl freind X is a fantastic anime full of comedy, romance, and mild mild ecchi. Theres also some mystery, I mean this whole drool business isn't a normal thing so there's got to be something else going on. Maybe even something supernatural.