Some things that suck about dual suspension:
1) A dual suspension bike will NEVER be as efficient as a hardtail
2) The front suspension may compress, but you have no rear shock to rebound while the front compresses, tossing you off the bike
3) You can out sprint everyone riding their 30+ pound full suspension
4) Your bike will ALWAYS weigh less than a dual suspension bike ever will
Granted, dual suspension has it's merit.. in fact I actually have one. But I end up riding my hardtail more than anything. At the end of the day the hardtail leaves me feeling much less worn out than my dual suspension does. But when the urban assault time comes around I'll be riding my dually.