Probably 2 years. Last time I was in downtown, I was on bikes and had rode down from Cedar Falls. I've been in the neighborhood SE of East High (between MLK and Franklin) in the past 5 years or so, and that was pretty bad.
They started that clean-up work last summer, a lot of those buildings you saw going that way are gone now and there are a lot of new stores going in now. It's not a terrible area anymore.