Slime has saved the day many times out on the trail. I ride in the deserts around Phoenix; some places we go are fairly remote, and it's a big bummer to get a flat 10 miles from the cars when it's getting up to 100 degrees in the shade. The beauty of slime is that usually you don't need to change the tube. All you do is remove the thorn or whatever is causing the hole, spin the wheel so the slime can fill it, get out your CO2 and give it some air, spin again, and you're on your way. I had a flat once that hissed loudly, and I thought, oh boy, the slime isn't going to handle it. But, it did!

However, you asked if the slime stays in the tubes, and does it make a mess. Well, yes, it sometimes is messy. I try to remember to always leave my wheels set so the stem of the tube is at the bottom, with the slime draining out. If I forget, sometimes the slime gets on the pump. Also, a couple times when I had major tire damage, such as when I picked up a 3 inch nail (On the trail! How'd that get there?). When the tires blow big, the slime erupts. But, no big deal, you just wipe it off.

The slime tubes really are worth the extra expense. When I've actually had to change the tubes, I usually find half a dozen little green spots where the slime took care of business for me.