[My Reply in Brackets Following Each Question]
1. Is it a plus to have a summer internship with another consulting firm at CV (level of ATK, Monitor, etc.) during full-time recruiting with McKinsey? Will it help an applicant to differentiate from other candidates? Will interviewer try to find out whether this internship resulted in an offer?
[I would say, yes that's generally considered favorable sign. The interviewer might ask if you received an offer... and it would be expected that the answer is yes. If the answer is "no" that would be a concern and might be worse than not having the internship at all. It sort of begs the question of what about your on the job performance resulted in you not getting an offer.]
2. In my case I will probably have 2 internships with different firms (one standard summer MBA internship and one pre-MBA internship as Summer Associate too). Is there a risk that I will get an image of hopper who doesn't know what he wants and just like case interviews?
[I don't think that's too much of a concern. It's quite common for people who go into consulting to not know what they want to do with their careers. When you ask most consultants how long they plan to say at the firm, the answer is almost always... I'm not sure... probably at least the next year or two.]
3. Should I tell my McKinsey interviewer that I have offers from other firms? Will it make me more attractive candidate?
[Yes, you should slip it into the conversation. I wouldn't brag about it or be arrogant, but just mention it in passing. It will definitely help a little... at a minimum it's reassuring that their positive assessment of your is correct. So if Bain and BCG both extended you offers, and my assessment of you is favorable... I'm going to feel that much more comfortable arguing for your candidacy in the decision meeting following your interviews.]
4. What does McKinsey think about entrepreneurship experience of candidates? I found out that many firms are very suspicious about it, so decided to get an MBA since after it applicants are "more standard products" for top consultancies.
[I'm not sure I can give you a good answer on this one. The MBA thing DEFINITELY helps as many candidates use the mba as a transition point in their careers from say manufacturing to consulting or the military to consulting. So if the entrepreneurship experience preceeded the MBA, I don't think that's necessarily a negative (though it may vary be individual interviewer). During the dotcom boom, there was definitely a concern that really entrepreneurial oriented people would not stay with the firm very long. In this economy, my guess is that's much less of a concern so I probably wouldn't worry too much about it since you can't really change it at this point.]