I feel it is very important to have something to look forward to. I rarely set goals but I reward myself along the way when I reach certain milestones. I have a long term goal right now to reach 200 by Christmas (actually 12/28). That is just under 40lbs away. This is the first real goal that I have actually set though in the 16 months that I have been at this. I am most motivated by clothing sizes it seems so I use new clothes as rewards. I try to only buy them every other size though because that way they can be worn from tight to too loose before spending money on more. If you do prefer the weight goals though I would probably go for the goals of 18lbs. That way you aren't always looking for the same number on the scale (280, 270, 260, etc) You could always be looking forward to something different (280, 262, 244, etc).
Haha! Sorry for rambling on...