I have heard of companies having official, sanctioned, mentorship programs. I would probably take advantage of such a program because doing so would make me look like a “go-getter”, but I couldn’t imagine it being a very good long-term idea. And the relationship would be extremely guarded while it did last.
I would not want a mentor within my law firm because I want someone with whom I can discuss what is best for me and my career, and at the end of the day, that might not mean staying with my firm. (It could also mean things like having to establish boundaries with a Partner in the firm, or something else unpleasant). I just would not feel able to speak freely to someone within the company. I also don’t believe in getting too close to anyone at work anyway, because at the end of the day they will do what is best for their own careers, and you never know where that might leave you or what might come back to bite you.
My relationship with my mentor is a give and take. He provides me with more support and guidance than I could have ever hoped for, but he knows that if he needs someone to edit something for publishing immediately, that I will get up in the middle of the night to do it. When entering into a mentorship, it is really important to keep in mind what you bring to the table for your mentor. It cannot be a one sided relationship.