NPR had a report about Pittsburgh's finances this morning. Short version - they're f'ed. One can't lay the blame on any particular thing - but one can lay it on two general things - a bunch of borrowing combined with a gradual erosion of the tax base. For years Pittsburgh has been basically exempting any big bizness that shows up from paying any taxes. Combined with the fact that the only commuter tax is only a flat $10, and a huge number of nonprofits don't pay any property taxes, what are they left with? City resident income taxes, residential property taxes, and... onerous small business taxes. So, big bizness is subsidized at the expense of small business. Suburban dwellers, who really do (Even more than many cities) use Pittsburgh city services, are subsidized at the expense of local residents.
Nothing short of a complete tax overhaul will save them.