Same boring problem.
Late 2009 15" MBP connected via Minidisplayport-hdmi adapter and hdmi cable, (both bought from Neet via Amazon) to 22" LG tv.
The mac sees the tv. It is added and removed in Display Prefs as I connect/disconnect the adapter, so there is some sort of communication going on. I have spent hours, including trying every possible combination of resolution and refresh rate in the Prefs pane - being careful to power the tv off and on again after every permutation. The tv constantly reports No Signal. I'm tempted to send it a clear signal with a very heavy object right now.
One thing I haven't seen mentioned here (or anywhere else) is the NTSC/PAL setting. Many of the available resolutions only allow 60Hz NTSC as a resolution. Anything else is greyed out. Here in UK our tv setting is PAL, not NTSC. Is this relevant when setting up a connection with the mac?
I sent an email to Neet cables, and I should say they have been great. Answered within a few minutes, saying they have sold thousands of these adapters and cables and not seen this problem before! They are mailing out a replacement adapter+cable today, and say that failures are v rare but not unheard of. However, because the tv is listed in the Display Prefs pane, I'm not hopeful that a new adapter or cable will help...we'll see. But this is definitely the kind of cust service that will take me back there again in future.
If only Apple would show they care too, and offer some wisdom here.