This is extremely similar to an idea I had the other day:
a) 100 XP to level up, regardless of your level.
b) Easy encounter: 5 XP. Medium: 10 XP. Hard: 20 XP. Deadly: 40 XP.
c) If you prefer quest awards instead of encounter awards, just pick the % of a level you think it's worth. Like, "This major quest is worth 2/3 of a level" = 66 XP. If you want, you could scale this up/down based on character levels, e.g., "This level 8 side quest is worth 60 XP at levels 1-6, 50 XP at levels 7-9, and 25 XP at levels 10-20." (You could do a smoother curve or just a direct linear scaling of [base quest XP * quest level / party level], but that gets kinda mathy and defeats the point of a simple "every level is 100 XP" system.)
Divide these numbers by 10 and you have [MENTION=463]S'mon[/MENTION]'s system, almost exactly (except I would be slightly more generous with the Deadly encounters because, uh, they're deadly).