Getting into a metal can bolted to a rocket is inherently dangerous. And even after you've escaped the full force of the Earth's pull, you're still not safe floating around in microgravity. There's radiation and the obvious nothingness that'll kill you in a few minutes if you're exposed to the vacuum of space. Assuming you're protected in a nice shielded spacecraft with plenty of food/water/air, you can spend months up there, but then you'll have problems getting back to terra firma. Survive the landing, and you may find out that your muscles have atrophied substantially. Here are just a few more links to possible challenges with manned space explorations.
If you'd like to read more awesome and interesting stuff, check out this unrelated (but not entirely random!) Techdirt post