im not sure about mech, it seems very difficult but so rewarding if you can pull if off, my main qualm is that tanks get destroyed by so much of the protoss army and they seem to be the backbone mech needs to work.
i have personally been using this build...
http://www.teamliquid.net/forum/viewmessage.php?topic_id=172190...in every TvP i've played lately and i havnt lost a game yet.
im not executing it as well as i could, and im constantly learning new little parts to the build, micro and timings.
on the whole its fairly amazing though, the army composition in the end is amazing, it actually feels so overpowered.
The crux of the build is that you FE with 3 full bunkers with marines and repair ready. then deny scouting with a raven and a thor (absolutely shuts down any scouting and also if they see you thor, they often suspect mech). You then get 4 starports pumping rounds of banshees and push with everything you have while expoing and getting a core.
Heres what ive worked out so far in terms of unit composition responses.
Spoiler
stalker heavy - you make sure to always have 1-2 ravens, and used PDD. it absolutely crushes them.
robo - not a threat in any way, your marines and thor will die, but your banshees and raven will live to destroy everything.
high templar - get cloak and spam it, have units ready to repair, split up your banshees when attacking so they dont clump for storm.
dark templar timings - you have a raven in time, you have ravens in your mix
cannons - PDD + insane dps of mass banshee.
Starport play - im yet to have a protoss react fast enough to get out enough starport units to kill me, if you deny scouting properly they shouldnt have time to react. probablly you would need more marines.
i have a few replays ill amend to this post, im mainly only playing mid-high diamonds though so theyre not amazing.