I've looked at the pictures of collections with 20+ bottles open and wonder how long will an opened bottle stay good? 6 months? 1 year? 2 years? 5 years?

I want to try many different bourbons, whiskeys, scotch, and even tequila (something I hated when I first sampled it 10+ years ago). Some of these bottles I may only drink from once or twice, but I'd rather not throw them away. How long can I expect for the whiskey to stay good? Do any of you throw away whiskey after it has been open for a set amount of time?