It is safe to run the software as a relay or client.
There is some risk of police busting down your door if you run it as an exit node. Generally it is not illegal to run it as an exit node although law enforcement in many countries are technically incompetent-or near so. They don't understand how the Internet works. When they do semi-understand they make arguments to the effect of Tor being an oddity. The problem is most users are running MS Windows and infected with malware. As a result running Tor as an exit node and having traffic for which is not yours is normal. Not to mention that until recently most wireless access points were unsecured. There are lots of situations where the traffic which passes through an IP address is not connected to the account holder.
