I purchased Discover 125 DTSi bike in August 06. It is very good and giving a average city milage 65 Kms / liter normal petrol and in highways it went upto 73 Kms / liter normal petrol. I drive usually in a decent way. In some occassions it gave me 69 Kms/ liter normal petrol in City driving.
It is very smooth and having very good cofort and control. I felt some occassions that it should have had 5 gears instead of 4. I was told that it came with Disk break in the beginning and later changed to Drum break as it was not perfect and caused lot of complaints. Though it is not Disk break, I feel comfortable in breaking.
I have been using bikes for the last 20 years. My friend is having Honda shine 125 CC Disk break. We used to exchange our vehicles often. It is also good bike. but I like Discover more than any other bike.
Bajaj gives better service and cheap spatres too. Definitely it one can buy with confidence.