United:
The gate agents generally do a Visa/Passport check prior to boarding. Be sure to have your Tourist Visa On Arrival (TVOA) documents all printed out. Especially the email you'll get from them saying it has been granted. I had no problems with this when I used it in March.
India: There will a special counter with signs directing you there. Again, be sure to have a printout of the "granted" visa email. Also, be sure to have a printed copy of your flight itinerary showing your return leg, as well as a printed copy of any hotel reservations. Life is also easier if you actually arrive in the port of entry you put in your application. I was initially scheduled to arrive in BOM, but had to change tickets last minute and ended up going to TRV. Luckily I had a printout of my email correspondence with the TVOA helpdesk explaining the situation.
When I went through, the process was a bit clumsy with half the computer systems/fingerprint scanners in TRV not working.