I bought my Tata Nano Twist XT on 1st February 2014. Have driven it for almost 1700 Kms now and got the 1st service done at 1500Kms(it was supposed to be done at 1000 Kms but I was caught up some place).
I have noticed, and my dealer has also reported other owners complaining about this, that there is some noise filtering in from the instrument panel(as if a small plastic piece is jumping around in a hollow space). Also, my use is mainly in hilly regions of Mussoorie and beyond and my little car faces problem climbing uphill in reverse gears if there are 2 or more passengers, though I had heard that a cars reverse gear is as strong as(and sometimes even stronger than) the 1st gear. Also, as I drive mostly alone in the hills(not yet Married;-), I notice a lot of body roll going around corners at over 40 Km/H.
Apart from this, I have not noticed anything negative. The space inside is amazing. I feel that our WagonR is more cramped now when I sit in it after spending the whole week in my Nano. It is quite tall, has a good ground clearance, the seats are nice and comfortable, it has a host of creature comforts to pamper you at such a small price. My car cost me Rs.2, 68, 174(on-road Dehradun, Uttarakhand). It has a RFID Tag for Automated Tolls on the windscreen, it has Bluetooth Connectivity for my phone along with USB and Aux-in in the integrated Music System, it has Distance To Empty(DTE), Average Fuel Efficiency(AFE), Remote Operated Central Locking, it has factory fitted everything, and I did not have to spend a penny on anything else as could not find anything more I wanted in my car.
I get a mileage of around 17-19 KMPL in Hills and almost above 14 KMPL even on steep incline roads. I get about 18-21 KMPL in Plains and I am very happy with my car. Our Wagon R(2005 model) gives 13-15 KMPL in city and >17 KMPL on highways. The ride quality is good, except for the body rolls. The music system has a nice sound quality and the Radio is capable of catching the Radio stations airing from New Delhi in my village even though it is not available through other cars audio systems in my area. The 2nd gear is tall enough for 20-60 KMPH and the 3rd good from 30-90 KMPH. I hardly need to use my clutch during braking, unless of course during a hard-braking. The car picks up effortlessly from braking to driving speeds without the use of clutch.
I have had the privilege of driving my car through snow-filled roads during this February snowfall in and around Mussoorie-Dhanaulti and it has never failed me anywhere. Being a rear wheel drive car, the front wheels steer effortlessly through snow and frost while the rear wheels push this tiny wonder forward. People stare at my car as it moves past them in the hills. Tata has done a marvelous job in making this little wonder, and it is appreciable. The place I work in was hit during the disaster last June(2013), and so the roads are not very good now. And the 180mm ground clearance is a boon in such a place when I have to drive through potholes, rocks protruding from the road surface, unpaved(kutcha) roads etc. The in-built fog lamps(a feature missing even from the top of the line Alto 800) are also a good feature while I had to drive through foggy conditions and clouds(in the hills).
Overall, my experience with my car has been a pleasurable one. The service intervals are at 1000Kms, 10000 Kms, 20000Kms and 30000 Kms. I got an AMC done during purchasing this vehicle for Rs.3200, so my Oil and Labour charges are free for 4 years. As freebies, I got floor-mats, mud-flaps, body cover and seat covers.
I would encourage anyone who likes this car but is not buying it under pressure from others to ignore their advice and go ahead to buy it. I had a lot of opposition from my friends and family too. Even my family was against my decision to buy a Nano, but when we went for a test-drive as a family with the Sales guy(and trust me 3/4 of us are heavy built and 1/4 is thin and even the sales guy was a little on the heavier side) and the car pulled off with the 5 of us on board with ease in the city. I have traveled with 4 people on board along with enough luggage(all 4 of us and the luggage would have weighed around 350-400Kgs that day) in the hills, and I have not noticed any problems except for the weak reverse gear that I have mentioned before.
As a city car, I am sure that it will not fail you. In the hills, if you drive carefully and know the limits of your car, I am sure you will keep out of trouble and this car will take you from point A to point B in all comfort and safety from the forces of nature. All in all, if you like this car, go for it. If you do not like it, you will always find something or the other to complain for. So, you can either love it or hate it for what it is, and that will affect your buying decision more than anyone elses opinion. Most people will advice you against it, even when they have not ever taken a test drive of this car. I would advise you to take a test drive and convince yourself, then only can you convince others as I was able to. Good luck!
[UPDATE]
I will be completing 4 years with my Twist XT on 1st of Feb. I have covered a little over 35000 kilometres in these 4 years. Have not faced any major issue in my vehicle. The windshield got cracked in Dec 2016, were still using it as it is, the crack has increased, but the windshield is holding on for now. I had opted for 4 years extended warranty, which will expire on 31st Jan 2018. No major ownership hassles till now. In this meanwhile I have got married and now have an 8 months old son, the Child Seat fits in the rear bench with the lap belt provided. I may keep my car for another 1 year or so, before upgrading to something bigger and safer. Hats off to Tata Motors for bringing out a product like Tata Nano. Wish they could give it safer body, active and passive safety features, bigger and powerful engine, and relaunch it on a newer platform. Id still buy it again if it fits all these criteria. I wanted to change mine for an XTA last year, but refrained.