We've decided to split ours. DW's adoption pay isn't brilliant where as the company I work for offers up to 5 months full pay for adoption leave. She also works in education so will be off work for 7 weeks over the summer.
So after the first 2 weeks, I'm taking the first block of SPL covering the end of the school year and the summer holidays, then in September I'll go back to work and DW takes the remainder of the SPL.
Financially it's tons better for us, but more importantly is will give us that time together as a family over the summer to fully bond and get used to our new life.
SPL rules say we had to give 8 weeks notice to HR of our intention to take SPL which we did as soon as we were informed of our match. At that stage were expecting it to take about 10 weeks to get to introductions. My HR were great, all the forms were available and they had some experts to guide me through it, and a few days after submitting it got a letter back confirming my entitlement and their agreement to my plan for SPL. Result!
As I said in the original post, DW has had a much harder time of it. No policy or forms in place so we cobbled together the information we had to submit with a covering letter and sent that to them, pointing out it had been legislation since 5th April so they need to either accept the letter or get themselves sorted quickly.
Anyway, things moved on pretty quickly after that, and panel date was brought forward by over a month, to mid May, with intros starting a couple of weeks after. 
The 10 weeks notice we had turned into 5. With it all being quite new we had no idea if we could change the SPL plan without giving 8 weeks notice. Turns out they do have flexibility to accept a shorter notice period within the SPL rules and as long as our managers were happy we could do it. All getting very very real!