Some studies into the issue claim cosleeping is not safe and should never be practiced, while others actually say that cosleeping lowers the risk of Sudden Infant Death Syndrome (SIDS). As bloggers, we're obviously not in any position to advise you what to do! Instead, we advise that you review the available data yourself and make your own conclusions.
We do, however, have a few tips and comments on cosleeping. I'll say immediately that I have always coslept with my babies and that they are still in my bed most of the time years later. We chose cosleeping for one simple reason: added comfort for everyone in the family. As a nursing mom, cosleeping is a lot easier in my experience. Everyone gets more sleep, and when my babies were sick, I would be able to keep a close eye on them throughout the night, easily waking up at the slightest noise they made (which can lower the risk of a young baby choking in his vomit, for instance).
Having said that, cosleeping can be dangerous, if done wrongly. Never cosleep on a couch with your baby because the risk of either falling off or getting squashed between the couch and the parent increases, depending which side the baby is on. Don't cosleep with your newborn in a water bed, and don't cosleep with your baby if you are a smoker or when you have had a drink. Don't cosleep if you use any medication that can impact your senses, like sleeping pills. If you cosleep, make sure heavy bedding and pillows, which can pose a risk, are not anywhere near the baby.
Cosleeping can be safe, in my experience, but it can also be dangerous. As with everything else, common sense should be applied.