Love this place. I try to get out to this gym every time I go to Vegas. The gym is located in an inconspicuous (which is surprising considering it's Mayweather) location in the Chinatown area of Las Vegas, a couple miles from the Strip and a little less than a mile from the Palms/Rio area.
Most of the time anyone can walk in and watch the boxers train. I've never seen Floyd there but every time I've gone either Floyd's dad (Mayweather Sr.) or his uncle (Roger Mayweather) or both are there training boxers. (They are there practically every day during the week.) They are very friendly and are more than happy to take pictures and sign autographs for anyone so this gym is actually one of the better photo-ops in Vegas.
Have also seen Jeff Mayweather (another of Floyd's uncles) and champion boxers Ishe Smith and J'Leon Love there on multiple occasions. At the end of the day, it's just a regular boxing gym but pretty cool to see a lot of the faces you see on TV doing their thing.
Roger especially is a real chill, laid-back dude. Has always signed stuff for me when I ask, though you really don't want to bother him while he's in the middle of a training session. He's really good with the young kids who come in with their parents just to look, making it a point to come over and say hi and even give a few introductory tips on box.
If you are a boxing fan would very highly recommend checking the place out.