I passed the SPCORE exam yesterday which rounds off the CCNP SP for me! Pretty decent exam, a lot harder than I remember the CCIP QoS exam being, especially as the SPCORE exam is now essentially the old QoS exam + IOS XR + MPLS TE. QoS is about 70% of the exam blue print so make sure you know how to do QoS really well in IOS and it won't be a problem at all in IOS XR as the commands look pretty much the same anyway.
Other than probably about 50-60 hours on the INE SP racks, I don't have a lot of exposure to IOS XR. Thankfully most of my job is in Junos so the translation didn't see that too hard to me (especially with remembering to commit!). I went through the INE SP workbook probably 2 to 3 times on sections such as MPLS TE, Inter-AS VPNs, and MPLS QoS to make sure I was comfortable with IOS XR before I jumped into the exam.
For anyone out there wanting to study for SPCORE, SPEDGE, I used the following materials:
1. IOS XR Fundamentals - an absolute MUST if you haven't played with IOS XR before
2. MPLS Fundamentals - excellent intro to MPLS, AToM, VPLS, and TE
3. MPLS VPN Architectures Vol1 - was okay, I didn't read all of it but the bits that I did read weren't too bad
4. INE SP ATC videos - excellent instructor went through how to do pretty much everything MPLS in IOS XR
5. QoS exam cert guide - great book on QoS
6. QoS-enabled networks - I haven't finished it yet but from what I've read it's really solid - thanks reaper81!
Good luck to anyone going for this cert, it was tough but well worth the learning experience. Happy to answer anything about my preparation for the exam.
Back to studying for R&S lab now.. 

Edit: and thanks to srg for answering all my questions about the exams!