Do used tea leaves have any value or hazard to house plants?

Yes, Brewed tea leaves make a fabulous fertilizer, both in your garden as well as helping potted plants indoors. Again, as long as you have not added anything to your tea such as sugar or milk, the brewed leaves contain high levels of minerals, carbohydrates, and other nutrients that create a rich soil. Mix your used steeped leaves in with your mulch or garden dirt, or add just a little into the soil of your potted plants and watch them thrive and grow larger!   In our article: http://www.teavivre.com/info/uses-for-tea/ , we introduced some unique way to use brewed tea leaves at home.

Tea leaves are a wonderful component for adding directly to soil, or for using in your compost. I'm lazy also - I just toss used tea bags, label and all, into my compost. (For the benefit of readers outside the US, compost refers to decomposed organics added to soil; the stuff in pots, and in which plants are placed in the ground, is what we call soil, or potting mix, or potting medium.)  And I can't think of any kind of herbs that would be bad for plants in any way. If people can drink it, I would think it would be okay,  but I wonder if anyone else has any knowledge to the contrary.

I always spread used tea leaves around the plants in my herb or vegetable garden. I have read that they provide a good source of nitrogen into the soil.