HELP! Odd Gel Pattern!!

[brunker at delphi.com]

    Instead of getting descrete bands on our electrophoresed agarose gel, we've
been getting "smeared" patterns...a dark band followed by a gradient of lighter
stains trailing back to the well. (I hope I'm describing this clearly).
    Does anyone know what causes this, and how we fix it? 
    These are PCR products digested by Nco1, and should produce not more than
three nice strips each, not counting the primer lines. The marker lane looks 
fine. The pieces we're looking at (we hope) are ~30, ~190 and `160 pb's.
    Has this happened to anyone else? Are we really producing an increasingly 
large range of DNA strands? 
    How could such a fate have befallen us?!!
    Thanks,
    Marla Brunker
    brunker at delphi.com