It's worth mentioning that VanitySearch than vanitygen is up to several times faster at finding private keys to vanity addresses:
On my Intel Core i7-4770, VanitySearch runs ~4 times faster than vanitygen64. (1.32 Mkey/s -> 5.27 MK/s)
On my GeForce GTX 645, VanitySearch runs ~1.5 times faster than oclvanitygen. (9.26 Mkey/s -> 14.548 MK/s)
If you want to compare VanitySearch and Vanitygen result, use the -u option for searching uncompressed address.
VanitySearch may not compute a good gridsize for your GPU, so make several tries using -g options in order to find best performances.
Using compressed addresses is roughly 20% faster.
Other links of potential interest:
Vanitygen Plus:
https://github.com/exploitagency/vanitygen-plus/tree/master/Hey thanks for the additional information - I'm looking forward to trying out the software sooner rather than later. I vaguely recall being PM'ed about VanityGen Plus, but got bogged down with other stuff and let it slide.