I sell tools for a living and deal with all the major MFGs, but if you know what you are getting and don't have high expectations, Harbor Freight has it's place. I have a few things from there, like a little mini portable tire compressor, and orbital polisher (with a coupon, I got if for like $30). For the price and minimal usage they fit the bill and you can't beat the price.
For air/power tools, tool boxes, and hard line items like sockets, screwdrivers, etc. I would not use them as the cheap pot metal and internals will fail pretty quick. Pretty much anything that will be used frequently or under rough conditions is out of the question.
For little nit noy crap like polishing bits, rags, etc. they are pretty good too. No need to pay full price for a polishing bit because it says Dremel on it. Their pads and clay bars have helped me polish up a good amount of stainless steel parts and not cost me an arm and a leg.
They also sell Meguires polishes and Evaporust, which is great. Best prices in town on that. I feel they have their place, if you know what you are getting.