Carpet is fab - keeps the "heat" in and a pleasant floor to walk around/sit on. We also have a Montana 6 canopy which proved invaluable this weekend as it's somewhere to cook/prep meals/and possibly sit in between rain showers. Our tent came off Ebay and came with the canopy. Think it's a good idea, given our lovely English climate!
We have a carpet for our Georgia XL, and love it. It means that you can get out of bed and toddle around without your feet freezing off. It is lovely and cosy for our DCs (3.5 and 21 months) to play on when it rains. Definitely worth it.
i was sceptical about the carpet but am converted - was fab for not so warm scotland! it was cosy and warm to walk on, I used the dustpan and brush to sweep dirt off and it stopped the chairs damaging the sig. Have seen the monty extension at a show and it looked good - made it more like a vermont.
I've just had our first trip away with an Outwell tent, and the carpet was great - echo what others have said. Despite very damp conditions it made the inside of the tent feel really dry and soft and lovely and warm.