The ACCP (Aviation Career Continuation Pay ??) is for those aviators who are at the end of their obligation. It's an incentive to keep pilots/NFO's in the military. It probably will not always be around either since the good economy in the mid-late 90's brought about its need. I'm not sure what the Marine's offer but the Navy offers a 3 and 5 year signing bonus. I just took the 5 year $125,000 bonus. A very good friend of mine and fellow aviator just switched from Navy to Air Force and accepted their 10 year $250,000 bonus.
To be honest, if this was the late 90's and the airlines were hiring, I would have most likely jumped on that band wagon. However, making anywhere from $105K to $110K (gross and obviously including my bonus) a year depending on my BAH isn't too bad for an 0-4.