Not tweeting, but I have been carrying on an email exchange with Dave Nachmanoff about guitar playing and music.
I read that the Pope is now tweeting on Twitter.
I tweeted once to the awesome porn star and geek April o’neil, whom replied back to me quite quickly. She’s pretty awesome.
OMG you got Kryten to smile! 
Michael Voltaggio answered a tweet I sent about sous vide, once. It was between Top Chef 6 and when he and his brother really took off with endorsements.
Andrew Zimmern randomly decided to follow me one evening while he was at an awards show.
I’ve gotten replies, RT’s, or DM’s from at least the following (I’m sure I’m forgetting some):
Rainn Wilson
Chris Hardwick
Kevin Smith
Rick Bayless
Stephanie Izard
LeeAnn Wong
Ted Leo
Hoodie Allen
Rhett Miller
Alpana Singh
Jen Kirkman
Kulap Vilaysack
Scott Aukerman
Kevin Smith once tweet. . . responded me. He was having a screening of his new movie for film reviewers and I made a clearly witty joke. I ended up getting invited to the private screening but couldn’t make it. 
Happened again. 
Asked about a local sports team, they responded within 10 minutes.
Gabriel Iglesias (the “fluffy” comic) told his followers that if they sent a @ message, he’d follow you. Got my 1st celebrity follower.
Just had conversation with Kristen from Top Chef about the accessibility of her restaraunt. (Boston area)
Not personally, but my friend has gotten more than on PM from tweeting Norman Reedus. She’s quite the fangirl and of course this completely makes her day. From what I’ve heard, he’s very good about interacting with his fans.
Not Twitter but e-mail. A few years ago I had a little crush on Deborah Norville when she had her own show on MSNBC (Can’t believe I used to watch that news channel!). I sent her an e-mail and she replied! I think it was her. Looked legit. I may still have the e-mail somewhere.
One of the first people who followed me on Twitter (total number is still less than 40) was Frank Stallone. I’m not sure if he qualifies as a celebrity though.
I am friends with Stephen Tobolowsky on Facebook and actually have interacted with him several times. He’s really nice.
I got a short reply from Emmitt Smith to one of my tweets. Since I expected nothing at all, it was a very pleasant surprise!
I have a friend who emails with D.C Fontana all stemming from his asking her about an old Trek PC game that was developed but never happened.
Just sent Jarah a tweet asking about a tatto she has.
I tweeted superstar DJ a Eric Prydz a question about which was cooler according to him, that Gucci uses his newly grammy nominated remix in their Blake Lively ad or that Rockstar used his “Pjanoo” in one of the spots for Grand Theft Auto.
He replied that “I don´t care, I just like beer”
Weird response I suppose. The day after he tweets a pic to his followers of him holding a mic in front of a crowd while another DJ is playing and writes:
“Oh god, don´t remember this at all. Hope I didn´t sing!”
:smack:
Me? I regard us BFFs now.
@ChrisKattan responded to me (and apparently several other fans who were bugging him about it) somewhat testily that if we had questions about whether or not he was going to return to The Middle, we should tweet some ABC twitter feed about it, because he had no idea.
@RalphieMay responded directly to me as well. I asked him if he still used edibles, since he’d had to give up smoking weed. He said he was off edibles as well, and boy did he miss it. Swell guy, that Ralphie May.
Also, @EricStonestreet will carry on long conversations from time to time, provided you’re talking about something that interests him. Seems he’s mostly about college football.
It was what I suspected. (she has her parent’s names on her arm)