My ex-T did, and she did so under the guise of "connecting". I think that forming some sort of relationship with your therapist is essential for therapy, but it must be a connection that remains within the confines of the therapeutic relationship. This T fostered an unhealthy amount of dependence on her and it caused a lot of problems, both during the time I saw her and also after when our relationship ended and suddenly, this person that was an integral part of my life just disappeared.

I think that it requires a very skilled T to be able to know just how much attachment to foster for each individual client and when to draw the boundaries.