I've never been mugged, but I did get robbed at gunpoint while at work once. This happened back in 1999 during my first semester of college; I was 18 at the time and working the afternoon shift until 9pm with my manager.
It was a pretty quiet day at work and had one final the next day, but it was for my English class and it was just writing; nothing to study so I went to work. Now, the store had been robbed before, but never like this. We had a problem with break-ins, and finally got a metal gate set-up for all the windows. (The last of these robberies was actually hilarious since apparently a big fat man broke the glass in the morning right before the store opened, ran inside, and stole DRAGONBALL Z VIDEO TAPES. He couldn't get the register open and his blood was on the counter from trying to break it open.) I guess the thugs had a problem with this, so they took a more direct approach.
I was sitting right near the entrance to the store playing Beatmania on the demo TV and my manager was a few feet away at the computer on the internet. Suddenly these three teenages come in, one of them pulls out a pistol, and says to give us all the money, etc. I'm kind of out of it at this point, so I turn around, look at him, say "man, stop playing!" and turn back around resuming my game. :lol That's when I hear the pistol cock and I realize this is no joke.
The guy with the gun tells us to get down, give him our wallets, then he tells the other two guys (who seemed even more scared then we were) to get the games and take the money from the register. They took a bunch of Dreamcast games and the cash, and ran out. I was freaking out because without my wallet, I wouldn't be able to get back into my dorm (it contained the keycards for the parking deck and the building/dorm room) that night, but luckily my roommate was home and was about to come down to work to pick me up.
I got really lucky, however, as when the cops finally showed up, they found my wallet lying on the ground right outside the store with everything still inside! My manager wasn't so lucky but I don't think he had any cash on him, so he just had to cancel his cards. The worst part of all this was that I was visibly shaken afterwards (when it was happening it didn't even hit me; everything went so fast) and still had to go to class the next day to take my final.
We hired a security guard after that for the holiday season, but nothing else happened. Can't say I ever felt safe with those guards anyway; most of them were pretty messed up in their own unique ways, but that's a different story entirely.
The store has had one more robbery since that time; I think it was a year or two ago when my co-worker was robbed at gunpoint by a lone robber who took the cash again. I'm not as worried anymore, however, since an EB Games opened across the street. Those guys have been robbed by more "professional" types at least 4 times already, holding them up with automatic weapons, hitting any customers in the store on the back of the head to knock them out, making all the employees load up their TRUCKS with inventory through the back room, etc. We pretty much figure why would they bother with our tiny crappy store full of used games when they can keep hitting the corporate store filled with new stuff?