This was my first time travelling to Nepal via India.

Air India was nice.  It had pretty good service.

"utousucks" is right about getting the boarding pass from Delhi to KTM.

As soon as you get off the plane they will take you to a lounge where you will have to wait till one of their staff comes and collects your passport, and tickets (paper/e-ticket), and then will return with the boarding pass.  This time they forgot to get mine but they did bring it.  This system is kind of confusing as you don't know what is happening.  They should at least let the passenger know on this kind of process.  I hope they will soon avoid this process.

Jet Airways on the other hand was different.  They had good staff and were attentive.  Thats the difference between govt, and private run carriers.

The flight was delayed but only for an hour(was nothing compared to the delta flight that was delayed for almost 8 hrs in JFK)...

I didn't had to do anything regarding the luggage.  It was checked in all the way to KTM.

I will update more when I return from KTM.

p.s. I had only 3 hrs of transit in Delhi...(depends on how you fly---I flew from US to London, and spent few days in London and then left London at 9:30 pm)

Good Luck...