I just bought a new house that was built on fill dirt that sat for
maybe 6 months prior to building. The builder built 8 houses on this
filled in area, 4 ranchers and 4 split levels with a full basement.

My neighbors that own the ranchers constantly have water in their crawl
space. Even weeks after it rains the mud in the grawl space is soft
and they seem to think it's coming from under the foundation.

My house has a basement, but I have recently noticed cracks in my
basement:
http://utseay.smugmug.com/gallery/683511/1/29640121

Could this be because the water is coming up under my foundation? What
is the best way to find out? Someone suggested to me to drill a hole
through the concrete slab and see if water comes through during a good
rain. Does this sound like a good idea?

If water is getting underneath my foundation - what possible problems
could I have? Is the best way to fix it by install a sump pump?