Update1: As some folks said in the comments area: in Mountain Lion (10.8.x), the tool also works!
Thanks to ./martijn we have a functional driver to PL2303 chip based devices (to enable a serial port over usb) in OSX 10.7. To install, you have to do some tasks in the Terminal app, nothing hard. But if you need to do this many times, it can be boring.
After completing the process, you can check if everything went well (connect now the usb cable) with the following command:
kextstat -b nl.bjaelectronics.driver.PL2303
The installer is included below, please check the md5 hash (PL2303 Serial-USB on OSX Lion.pkg) = d6e1a52f2fdbde55bab716037c9630f7