How much can I depend on Tor for anonymity? Is it completely secure? My usage is limited to accessing Twitter and Wordpress.

I am a political activist from India and I do not enjoy the freedom of press like the Western countries do. In the event my identity is compromised, the outcome can be fatal.

Tor is better for you than it is for people in countries whose intelligence services run lots of Tor exit nodes and sniff the traffic.  However, all you should assume when using Tor is that, if someone's not doing heavy statistical traffic analysis, they can't directly correlate your IP with the IP requesting resources at the server.

That leaves many, many methods of compromising your identity still open.  For instance, if you check your normal email while using Tor, the bad guys can know that that address is correlated with other Tor activity.  If, as @Geek said, your computer is infected with malware, that malware can broadcast your identity outside the Tor tunnel.  If you even hit a webpage with an XSS or CSRF flaw, any other web services you're logged into could have their credentials stolen.

Bottom line, Tor is better than nothing; but if your life is on the line, use a well-secured computer for accessing Twitter and WordPress using it, and don't use that computer for anything else.
