Optimizer + bind variables

Does/is it possible for the PG optimizer come up with differnet plans when
you're using bind variables vs when you send static values?

like if my query was

select * from users (add a bunch of complex joins) where username = 'dave'
vs
select * from users (add a bunch of complex joins) where username = '?'

In oracle they are frequently different.

if it's possible for the plan to be different how can i generate an
xplan for the bind version?

Thanks!

Dave