Hi, I attended the interview and got selected
Here's my experience (some details might be missing, happened about three weeks earlier)
First there will be a written test,around 350-450 (I think) people would appear in that. The test was of half an hour and consisted of 7-8 questions and you've to attempt 5, I think. The questions were subjective type and you also have to submit your rough work sheet (professors are interested to see your thought process). There was one question from linear algebra, one the output of the program, one was from combinatorics, one from probability, one was discrete maths and so on.
The same evening results were announced and around 50 people were shortlisted. There are actually 15 seats for general category (going by this year).
Next day we had interview, Interview would be about 15-20 minutes. They'll be asking quite basic questions and would be interested in mainly how you deal with the problem. They asked me to choose subject, I said discrete maths I was asked a sum of GP question (maybe it was not visible at first site that it was a GP) and then there was a question on linked list and I was asked to write pseudo code.
All in all it's a fairly easy interview if you're good with your fundamentals and can write a bit of code.