We did it. We swapped over at 8 months. I breastfed until DS was nearly 2, it really wasn't a problem. (he did feed half the night at first, though...)I'm pretty sure the mother has to take the first 2 months, which is to allow time for establishing breastfeeding and physical recovery. It really gets my goat when people trot out lame arguments about men not being able to breastfeed as though it's proof that nature has made it impossible for men to care for their own children! Really, once you're through the initial constant feeding phase, it is a non-issue, surely. Not to mention that the majority of people don't breastfeed for very long anyway!
It was incredibly easy to arrange, just one simple form to fill in and sign a few months before you planned to swap over the mat/paternity duties. As far as I recall, the second person takes over rights to maternity pay etc as if you were the same person, so no additional benefits but no losses either. Of course, you might get individual workplaces offering more, but we both work in the public sector and were only eligible for the statutory minimum.
We now both work reduced hours and take turns when covering things like child illness, which works really well for us and means we are both an equal(ly small) burden to our employers!
Child number two is on the way, and we'll be doing the same again.
Slightly different subject, but I am truly amazed that most of you have said that your DP earns significantly more than you. Really? How come? Assuming the majority of people are in a relationship with someone of roughly similar educational and social background, with similar length of time since entering the job market, how have you have ended up earning significantly less? (I am genuinely interested, not having a go at anyone- are there reasons for the pay gap other than sexist employers and lower pay for "women's work"?)