Well, I'll chime in to say that Oolong tea can definately be brewed many times in succession. Usually 4-5 times. This is assuming you use enough leaves and the proper method.. which goes roughly like this:
1. Fill your tea pot/cup/bowl with near-boiling water. It's heated when the outside surface it uncomfortably hot to the touch. Drain the pot and discard the water.
1. In a small pot (like YiXing or GaiWan), use one or two teaspoons of dry tea (more for the light, space consuming loose leaf, and less for the compacted bundled sort).
2. Fill the pot with water just below boiling. Allow to sit for about 5 seconds, while agitating the leaves slightly. Drain and discard the water from the leaves.
3. Fill the pot again with water just below boiling. Allow to steep about 3-5 minutes. Drain the tea into a second (preheated) pot or into the cup you'll drink it out of. **Don't leave water with the leaves or they will continue to steep and become bitter**
4. Repeat step 3 until the leaves can't brew a good flavour.
This sounds a little complicated if you're not familiar with it, but really it's easy. In breif -- preheat the pot, use enough tea, rinse the leafs with a very short brew of hot water, seperate the leaves from the water after brewing by pouring off the tea so that they don't continue to brew.
As for how long you can leave the teas afterwards? Well... I will admit to having left wet tea leaves out all night, and then using them again the next morning without any problems. Be sure to drain all the water away from the tea after brewing. If you leave them sit in a puddle of water, they will mold very quickly. If you drain away all the water, and even give them a push to sueeze out the excess water they've absorbed, then they will probably be fine sitting out all night. I've even seen loose-leaf Oolongs like say.. Dan Cong return to thier almost original dried condition, and be completely reusable days later. Soo... Your Mileage May Vary.
In general I don't, and don't suggest, letting tea leaves sit around for very long. A hour or two is fine.. more than that, and you're taking a risk.
Hope that helps,