Well, people I at least consider celebrities
Talked to in person while working on a TV interview show- Danny Boyle, Alice Eve, Krysten Ritter
Saw in street, restaurant, theater, etc.- Martin Sheen, Emilio Estevez, athlete Alex Rodriguez, Cameron Diaz, Terrence Howard, Patton Oswalt (had gone to a performance of his the other night), Zac Efron
Saw at NY Comic-Con
-Speaking at panels- McG, Jared Padelecki, Derek Mears, Chris Evans, Clark Gregg, Cobie Smulders, Mark Ruffalo, Tom Hiddleston, producer Kevin Feige, Saoirse Ronan, Eric Bana, Joe Wright (asked a question), James Franco, Danny McBride, Thomas McCarthy David Gordon Green, Justin Theroux, Joel Edgerton, Adewale Akinnuoye-Agbaje, Eric Christian Olsen.
-Sighting- Tim Roth, Bill Hader
Have seen speak/Q&A- Production designer Bridgette Boch, cinematographer Ellen Kuras, Spike Lee (asked a question), John Boorman, Ryan Fleck and Anna Boden, director Drake Doremus, Felicity Jones, Lee Daniels, Jason Reitman, director Troy Duffy, Jay Cocks, writer Jim Taylor, Aaron Sorkin, Jonah Hill, director Jared Hess.
More are coming to me as I type this. But yeah, a lot of sightings/events. Not really 'encounters' per se.