Why is NFS not allowing me to mount a share?

Okay, I've worked it out (or at least, I've made it work, and I think I know what was causing it).

I added the insecure flag to the /etc/exports line on the NFS server, so now it looks like this:

/media/storagedrive 10.0.0.0/24(rw,sync,no_subtree_check,insecure)

This flag allows connections to originate from client ports above IPPORT_RESERVED (1024).

The mount command now works.

My guess as to why the lack of the insecure flag was the problem is that VirtualBox was using NAT to pass the request through to the physical network, so while the port on the Ubuntu guest (AlexDevGuest) may have been below 1024, the translated port on the Windows 7 host (AlexDevHost) was probably above 1024, and therefore blocked. Setting the insecure flag meant it was allowed though.

This problem obviously doesn't affect the non-virtual machine DevMatt.