To offer a USN counterpoint from my "brothers in blue," there are a few things to keep in mind.
1. Become an officer to be a leader of men and a defender of freedom and the American way of life. Uncle Sam may decide that the best way you can do this is at the pointy end of an F-18, or he may decide that you can best serve as Officer of the Deck on a Frigate. If you absolutely have to fly, just realize that you may be rolling the dice. Some OCS programs may give you a guaranteed flight school slot, but that may be as an NFO as well, as was my case. Don't get me wrong, I loved flying as a 'FO, but my 1500+ hours flying in combat and crappy weather in EA-6B's count for exactly squat!
2. The flying is incredible. You will do things that will raise the hair on the back of your neck every time you fly. 500+ knot low levels. Dogfighting. Large force exercises involving 60 or more aircraft in close quarters, at night, lights out. Cat shots. Night traps. You will be able to tell stories about at least one time that you almost got killed. You will be exhilarated, and at times, terrified. At the end of the day, you will have a cadre of brothers to share a beer with, and discuss how you can't believe they pay you for this! However:
3. In the USN (and to a certain extent, USAF), flying is a collateral duty, i.e., not your primary job. Your primary job will be as a maintenance division officer, schedule writer, watchstander, personnel officer, etc. This in itself is extremely rewarding, but it is a leadership role, not flying. Some people don't like being a leader/manager.
4. The Navy is all about command at sea. To this end, you will be expected to take "challenging non flying" assignments to develop professionally and to become more well rounded. I was active duty for 10 years, 5 of which were spent flying. The other five were instructor duty (shore tour) and a "disassociated sea tour" as a Tomahawk Strike Planner designed to make me more well rounded. This is typical. Seldom do junior officers do back to back flying tours, and it is likely that you will spend a good deal of time out of the cockpit. This is one of the reasons that I decided it was time for me to leave active duty.
5. I enjoyed my service greatly, but, at least from Navy perspective, go into it with your eyes open!:rawk:
EDIT: To answer your question about hours, most guys in my sqn flew about 1000 hours during an average 3 year tour. That would include at least one 6 month cruise or equivalent deployment.