The reason that you were not able to spoof your source IP address is probably because your ISP uses uRPF (Unicast Reverse Path Forwarding) or some other type of IP validation filtering before routing your traffic.
uRPF Info: http://www.cisco.com/web/about/security/intelligence/unicast-rpf.html
Quote block from the uRPF page on Cisco: "Network administrators can use Unicast Reverse Path Forwarding (Unicast RPF) to help limit the malicious traffic on an enterprise network. This security feature works by enabling a router to verify the reachability of the source address in packets being forwarded. This capability can limit the appearance of spoofed addresses on a network. If the source IP address is not valid, the packet is discarded."
Since you're not using a sketchy ISP that does not provide these services, you're not able to spoof your IP address successfully. At this time, IP address spoofing can be exploited on around 25% of ISP's worldwide (http://spoofer.caida.org/faq.php.)
The biggest issue is that there is no way for legitimate ISP's to verify that all inbound traffic is legitimate (not spoofed).
You're looking for spoofing stats? Here's the place to look:
You're wanting more info about spoofing and why it's an issue? Here's the place to look: http://spoofer.caida.org/faq.php
Also, if you're looking to test to verify that your ISP's DNS servers are not vulnerable to DNS spoofing, check out GRC's DNS Nameserver Spoofability Test: https://www.grc.com/dns/dns.htm