I bought my Wagon R- Duo last month and have just finished driving about 700 km. As such there has been no problem.
The main issue that is bothering is that even after three fills, the LPG tank maximum fills only 13 - 14 ltrs though the capacity is 22 ltrs. Is this an initial problem that would be rectified in the first service, I am not aware. Also the LPG gas meter is misleading. It comes down to amber pretty quickly and I am not sure how much gas is left.
The second issue is the gear shift. It is quite bad, especially for the reverse and the fifth. Is this an inherent MS problem? My earlier M-800 also had this issue.
I am pretty happy with the pickup in LPG(does not differ much except maybe when overtaking). Also the AC is very good. The mileage seems to be good. Have not looked at it in detail, but I think it gives around 10.5 lts per litre in LPG. Should go up after first and second service.
Overall, I think its a good city car especially for people like me who have to drive a lot and usage is high.