I use these XLR connectors every day in the Sound and Lighting business.
3 pin - for Audio inputs & outputs like Microphones and Mixers
4 pin - for Automated color changers that fit theatrical lights
5 pin - For the digital DMX control signal between console and Lighting
These connectors are very reliable, if there is a problem it is almost always something wrong with the wire or the solder connection, but not the connector. I never knew the amp capacity of the pin connections but the PDF I found on the Neutrik.com site that dinges posted has the following information...
3 pin: 16 amp
4 pin: 10 amp
5-6 pin: 7.5 amp
The PDF also says that they are rated to Connect/Disconnect 1000 times. I would say that it is 3 to 5 times better than that. They would not last very long if you plugged them while under load. Arcs will pit them pretty bad. Microphones output millivolts, Sound or Lighting consoles output up to 10 volts, Color Changers output up to 24 volts. The amps on all these outputs is quite low, less than .1 amp. If you tried to disconnect a hot load of 10 amps it would eventually become unusable.
XLR connectors are great because they lock together and are easy to unlock to pull apart. Neutrik connectors are very easy to use but cost a little more. Switchcraft connectors are really a better connecter but are harder to solder and assemble.