UPD 2: Round B is this Sunday (May 7th) — 5.00 GMT. Time
UPD: Round A is this Sunday Mar 5th — 5.00 GMT. Time
For problem difficulty, you can see previous year's GCJ APAC.
This year, it has 6 rounds (you can see them in the Schedule above).
For university students, this is a good chance for applying to Google.
If you have high rank in these rounds, you will automatically pass the 1st phone interview round (which might be difficult for competitive programmer, e.g. flashmt failed his phone interview =)). If you have good result, you will get contacted by recruiter. You can see more details in FAQ.