Ali you are blinding me with science.
Simple terms please
The basic Pocket Wizard Plus II is a radio transceiver that will fire a flash or camera remotely, at some distance, in bright light (unlike optical systems) and even through walls. You need two, one on camera and other on the flash. They fire either off the camera's x-sync, or manually off the button. US and EC versions are incompatible as they use slightly different frequencies.
They are expensive US made and while some are critical of the build quality, they have an excellent reputation for reliability. They also have a high-speed processor which means there is no reduction in x-sync speed, unlike most (all?) cheaper radio triggers.
TBH, for most people I don't see they offer any advantage over the Yongnuo RF-602 for a tenth of the price (not to be confused with the even cheaper 'ebay' RF-04 type which don't work with some flash/camera combinations). I have both and will be selling my PWs as they are incompatible with my five RF-602s, which are a neater design and like the PWs can also be used as a camera trigger with the cord supplied. Only slight drawback that I have found with the RF-602 is a slight reduction in x-sync speed, down from 1/250sec on my Canon 40D to 1/200sec.
The new TTL metering Pocket Wizards are altogether different, only Canon E-TTL at the moment - Nikon has been delayed, promised early next year. These things are amazingly clever and promise to do everything that E-TTL does, and a few extras (like Hypersync - even higher x-sync than normal) plus all the other advantages of radio triggering.
Unfortunately, they have been fraught with problems, in particular RF interference from some Canon flash guns which effectively reduces the range to little more than you get with Canon's own built in optical system

The solutions they have come up with, including a massive shield that fits over the flash, are unimpressive. Unless Canon (and others) decide to supress the RF radiation of their guns internally, I think PW will have to change their frequency to make them work properly, but that would mean old and new PWs would be incompatible.
Good timing with this thread
I've been looking at PW's for a few days now... I like the idea of using them for remote shutter release as well as flash but realistically I would probably never use that feature.
The reports of shoddy build quality on the PW's is probably what puts me off more than anything. I've had enough cheap n nasty radio shutter releases to know exactly what people are describing... which is ok, because for 12 quid I don't expect it to be built like a Rolls Royce but for 300 quid I do...
The AlienBees Cybersyncs seemed to get very good writeups but it seems the manufacturer has become all xenophobic and now won't ship outside of the USA.
Give the Yongnuo RF-602 a punt - £28 a set from FITP gotta be worth a try with the camera cord.
Radio Poppers?