Cisco has released recently lot of materials to be friend with their new technologies. You can know learn more about IOS XE with Cisco CSR1000v (it is a virtual router based on Cisco IOS XE code) and more recently (02/07/14) you can download Cisco IOS XRv 5.1. You can download it as a demo version (2M of bandwidth, AAA preconfigured, … : some restrictions). It is a virtual machine that you can import in VMware ESX VM.
I think it will be really great to learn, practice over IOS XR without any risks (for those of us who can log in some real ASR9000 or CRSX3, …).
More information :
A really, really good documentation :
I urge you to read this PDF… Thank you fryguy !