Alex hit the nail on the head. The doors are all plug type doors. I know that they seem to open outward, but the reality is that they open inward first, and then angle themselves slightly so that they will swing outward.
At altitude, the cabin is pressurized to around 7-9 PSI, which means that a gorilla couldn't force the door open. Keep in mind that 8 PSI in the tires of your car can hold the car up---of course you'll go through the tires quickly. And keep in mind that the 8 PSI is applied to a door that is approximately 72in x 50in yielding (I'm not a physicist or engineer, but I believe this is true) something in excess of 30,000 lbs of force on the door.
I forget the accident, but about 10 years ago, an aircraft landed with a fire on board, and for some reason (crew incapacitation, malfunction, etc.) the aircraft couldn't be depressurized, and no one could get the doors open to get out.
The FAA allows airplanes to pressurize on the ground, but to allow for the possible evacuation while still pressurized, the pressure may not exceed .0125 PSID.
If a door out due to structural failure, then depending on what other components it took with it and how close you were, you might find yourself skydiving without a parachute.
There is no blood boiling, emboli, or other medical problems, in a normally healthy person other than possible burst ear drums and just plain breathing. If you are stuffed up, you will probably blow holes in one or both ear drums; don't worry, they will usually repair themselves.
Breathing is different sort of problem. The time of "useful consciousness" can vary from several minutes to just a few seconds depending on your physical condition, smoking, age, and most importantly the altitude where the rapid decompression occurs. Once useful consciousness expires, they you are still alive, but it is like you are real drunk. You won't make rational decisions, or have any sort of reasonable coordination. Without O2 soon, you will probably die. This is why FAs always tell you to place the O2 on yourself first before placing it on a child. If you diddle with them, then you may save them, but kill yourself. If you start with yourself, then you have some time to get their mask on, as well as the ability to make certain that they keep it on.
One last point. If you are a SCUBA diver, and have been diving within the past 12/24 then a cabin pressurization failure can have real hazardous consequences. The Aeronautical Information Manual (AIM) states:
The recommended waiting time before going to flight altitudes of up to 8,000 feet is at least 12 hours after diving which has not required controlled ascent (nondecompression stop diving), and at least 24 hours after diving which has required controlled ascent (decompression stop diving). The waiting time before going to flight altitudes above 8,000 feet should be at least 24 hours after any SCUBA dive. These recommended altitudes are actual flight altitudes above mean sea level (AMSL) and not pressurized cabin altitudes. This takes into consideration the risk of decompression of the aircraft during flight.
Personal knowledge, B737 AFM, AIM