I had brought a 42" LED TV from Dallas to Bangalore. The comments in this thread has helped me a lot and thought will share my experience:
TV - LG LM6200 - 42" LED 3D SMART TV.
Flight - British Airways.
The voltage conversion was not an issue because the TV supported 100-240V, 50/60Hz. - Make sure you check this in the specs before buying this. Many models are offering thus.
The transmission is India is PAL while Most US TVs support NTSC. Make sure you buy a TV with HDMI port (Most TVs have now) - and get a DTH HD box (I took videcon). It has an HDMI outlet and works perfect on the TV. You need to get only normal HD set top box and not a HD - DVR as mentioned in many posts. Both have HDMI ports and the frequency can be adjusted in settings.
Make sure you pack the TV well - I got this packed by UPS (65$) - as they will just toss it during flight changes and there was sharp piercing @ the center when I got it in Bangalore - thanks to the good packing - TV was intact.
The check in baggage limitation in BA was 81" overall. My TV was 82" overall (packing dimension - W+H+L) - LG mentions this in their specs sheet - so you will know how big it is in advance. The airport staff will not physically measure it - He 'll just place it on the reception and see if it crosses the length of the belt- if it is within that, you are in - the choice largely depends on the staff. Also, B.A allows upto 109 inches by paying an extra (roughly 60$, same as overweight baggage).
The biggest problem is in bangalore customs. You are entitled to carry upto Rs.35000/- worth goods without paying duty. So they will charge you (Price of TV in India - 35000) *duty %.
For my TV, the price in India was 86000/- (Yes, they have sheet of Model - Price for most popular TVs; you can get the price in India by searching in some online sites like flipkart). I was asked to pay (86000 - 35000) * 15% (approx, not sure about actual %) = 7500/- as duty. Considering that I got the TV for ~38K + 3K (packing), it was still worth it. When I said it was a used TV, they asked me the bill (if you have one, carry it), but I said I forgot and negotiated for sometime, for which they applied some 6% depreciation (< 1 Yr use). Again they amount was reduced to 6K.
I said I had only 40$ in hand and tried negotiating. They gave out options like "you can keep it here, and collect within 2 months when you have the money" etc.I was not ready to pay, neither leave it, so again negotiated. After sometime, the officer threatened of noting "duty not paid" on the passport (he even took my passport, opened the page, and dotted with pen). I kept on negotiating and had a feeling he will not note in passport. All my co-passengers left by then it was almost an hour. Finally, I got the lucky question - "How much can you pay?". I said I can 20$ more from my friend and pay 60$ total. he agreed to it, I remitted the money, and got clearance - Happy

And one most important thing - If you have a TV, they will be only looking at it. They will never check your luggage for laptop, Mobiles etc. Carry as much as you want.