I bought one of these for pretty cheap ($30-50 range if I remember). But watch it, just googling for that link I saw on site for $250 and another for $50.
http://www.lenkeng.net/showproduct.asp?id=64
Otherwise it works exactly as advertised (Yes it comes with the HDMI Cable too). I hook it up to my 42" Plasma with HDMI cable ... when on the XMB its fullscreen as normal and when you go to a game its black bordered like most people say, then you press a little button that on the end of the cord going into the PSP and it does its little upscale process. If you mistakenly press it on the XMB or go back to the XMB you need to press it again or you get a super huge zoomed screen that you only see like 1/2 of.
As for the upscaling, I only used it when playing Final Fantasy Tactics (screen was soooo small on TV without this upscaler) so I couldn't tell if it actually made the picture any better as FFT isn't exactly a graphcal wonder.