Pros: 1. You'll be eligible of getting* a Premium Credit Card (Infinia/Diners Black or at least Regalia). If you already have one, you can be upgraded to higher one.
2. You'll get Classic embossed Platinum Chip Debit Card at nil annual charge with enhanced features.
3. No charges for usage of HDFC Bank as well as Non HDFC Bank ATMs (Domestic).
*As per RBI guidelines, currently HDFC isn't issuing credit cards to new customers.
Cons: A minimum Average Monthly Balance of Rs. 1 Lac to be maintained (NA for salary Account holders). One of my branch officials mentioned, charges for not maintaining AMB is nil. Same is mentioned in HDFC site as well. (not sure, how that contradiction works).