I just read about this. US Citizenship and Immigration Services (USCIS) received 163,000 applications for H1-B visas by April 7. Since that number exceeds the visa cap, the government will not consider any more applications this year (Source: USCIS, via the H1B data blog). 31,200 of the applications were from individuals with an advanced degree. The government quotas are: 20,000 for applicants with an advanced degree and 65,000 for the rest. (I wrote about the H1-B visa system a couple of weeks ago.)
The USCIS will hold two lotteries this week. The first one is for applicants with an advanced degree from a US institution (MA or higher). Applicants who are not selected in that first lottery will be pooled with the rest of the applications in the second lottery.
Unless my math is failing me, the probability of getting a work visa is then 80.4% for advanced-degree holders, and 45.5% for the rest of the applicants.
UPDATE: I'm really behind on this. USCIS already conducted the lottery (they did it on April 14, two days ago). Lucky applicants should get a notification by early June. I really recommend reading H1B data if you want timely information.