I am traveling from Rochester, NY to Heathrow through Newark on Virgin Atlantic. Continental (operating first leg of the flight) has changed my flight times and my layover in Newark is now just 2 hours. Will I be handling all of my customs matters at check-in in ROC? Or doing it at Newark? If the latter, will this period be enough time? Thanks.

You don't clear customs leaving the US. You will clear UK customs upon arrival in Heathrow. Virgin in Newark will verify that you have your passport with you. You will clear through security at Newark but its not US CBP.

Except for a very few exceptions (Ireland or Canada to the US) you must go through Immigration upon entering a country - not leaving it.

You always go through Customs (luggage) on entering the country.

All you need to leave the US is to show your passport to the airline gate agent.

From the US to the UK you will, after arrival at Heathrow, go through Immigration, then pick up your luggage, then go through Customs.

As everyone said - you don't go through customs here, and you'll be absolutely fine with 2 hours. You check in at ROC, the gate agent will check your passport and you'll get both your boarding passes if you booked it through Continental. You get to Newark, just get to your next gate, and you're good to go - luggage is checked all the way through. Enjoy your trip!

Be sure to check ahead whether you can checkin for your VA flights at the ROC airport. (Call CO or VA). If you cannot, then be sure to use online checkin before leaving your home. You don't want to get to EWR (perhaps even late arrival) then have to go to VA to checkin for a boarding pass.

If you are flying the same route back again you will go through customs at Newark on your return, before carrying on to Rochester, so make sure you have enough time on that transfer to cover it.