BlackVPN seems to be a good barebones VPN network. For the PC it uses that standard OpenVPN client for Windows with custom scripts. Its DD-WRT implementation is similar in that its script based. Using their directions and some copy and pasting the installation worked the first time though it required going through multiple menus. Changing servers is accomplished by changing the start up script and rebooting your router. To ensure the VPN is up you need to check your public IP address before and after (and during).
I tested their system in Europe connecting back to the US and it worked well enough to stream video, but back in the US speed was not good (The server I got assigned during the test was in Nevada resulting in a download speed reduction of 94% and upload speed of 50%).
BlackVPN is well reviewed on-line, so they might just be having a bad day, but a low speed connection is a low speed connection.
They have servers in a number of countries with P2P available on some of them. To get the most out of the system (P2P, local encryption, etc) you need to rock the Global Package for 1 Month €9.50 - 3 Months €27 - 12 Months €99
They offer a 14-day full refund if not satisfied and generally keep your information anonymous unless you P2P on a non-P2P server.
All in all BlackVPN is a nice little service, but probably not the first choice for DD-WRT use.
Disclosure: SecureRouter.Org is NOT a BlackVPN affiliate.