It's not so much the keyboards I love, which are great. Just read everyone elses' entry for that.
No, what I really love is the community. I joined GH at a very low point in my life, and just having people to talk to about something I love (mech keyboards) helped steer me away from the pit of depression I had been sinking into at the time. I had just moved across the country, had no friends or acquaintances. GH gave me an outlet for some semblance of social interaction in a period of utter isolation.
Whether you are talking about caps, boards, or clacks GH gave me a place to sort of open up. And doing so not only helped me meet a bunch of new online friends, but also helped me gain a wealth of knowledge about mechanical keyboards as well. And the more I learn about keyboards, the more I love them, which is a peak I would have never been able to reach without the knowledge and support of the people on GH.
On top of all that, my fingers now recoil in horror whenever I must type on a rubber dome. Once you've tasted a Ferrari you can never go back to eating a Camry... or something like that.