Well, we're doing it just now 
.
I went back to work when ds2 was 6 months old, basically when my additional mat pay came to an end. As dh earns less than me, it made sense for our family for him to take the next 6 months off.
If he couldn't have shared the leave then we probably could have managed the following 3 months with me on SMP, but I'd definitely have had to go back when ds2 was 9 month. This way he gets a parent at home for his first year.
It was pretty straightforward from my end. I just gave my work notice that I was returning early (I'd originally said I was taking the year in case anything went wrong). Apart from buggering up my pay the first month back as this hadn't got through to payroll 
, it soon felt like I'd never been away.
With dh's work it was ok in the end but they were clearly confused by the whole concept, couldn't seem to get that this was a statutory entitlement and not something that they could turn down, and had no policy to follow so were extremely vague about the paperwork.
Less that a fortnight before I was due back to work they came back to us with a flurry of demands for extra documentation which was obviously very stressful. It was all sorted out though and dh got his first SMP payment on time.
If they'd thought about this in advance and produced a checklist for the documentation they needed (they wanted more than what's strictly needed for HMRC purposes) then it would have been much easier.
There are several men at dh's work who are planning on doing this so hopefully it'll be easier for them.