LECOM,
I think you and john are confusing deployments with Permanent Change of Station (PCS). Deployments are done in support of an ongoing operation or exercises such as Operation Enduring Freedom (Afganistan). Deployments by regulation (at least AF regs) are less than 180 days (unless it is a deployment to fight a war, in which case you may be there for the duration). Families are not allowed to accompany you on these for obvious reasons (you don't want your wife and kids running around in a hostile fire zone). PCS's on the other hand are when you get orders to move to a new assignment/post/base permanently. The gov't pays a moving company to come and pick up your stuff and move it to your new "home", or they will pay you to do it if you prefer and it is within the CONUS (continental U.S.). Nearly all PCS's are accompanied with a few exceptions to remote locations, these are typically much shorter in duration than a typical assignment (usually 12 months as opposed to several years for an accompanied).
Since the Gulf War we have been deployed more than all the years between WWII and the Gulf War combined. We have been doing all these new deployments (i.e. Saudi, Turkey, Panama, Granada, Somolia, South/Central America,Bosnia, Afganistan, Philippines...etc) with an ever decreasing number of people in the military due to cuts in force numbers. This means we are doing much more with much less (something like 1/2 or less the amount of people in the military as we had at the end of the Gulf War). What this means to you is that your likelyhood of being deployed during a 4 year stint in the military is very high, and with the widening war on terrorism that likelyhood is only going to increase since it doesn't seem likely that any of the other ongoing operations are going to go away time soon.
Hope this clears things up a little for you...