Be careful of answers from "real estate" sales people, like those who answered your question -- they are all uneducated sales people who are hooked on this fantasy that property is a good investment and prices always go up. Be careful with "rent" assumptions, most investors are findig it very difficult to rent right now for reasonable income. Journal Square -- I would say its still a very rough neighborhood in parts -- it was a "up and coming" area in the boom economy years but could be very risky in the short term. I would wait until there was more signs the economic downturn has leveled off before investing in that area in particular.
My guess is it will be the hardest hit and the last to recover. In general, the best advice when looking at neighborhoods is to do the due diligence yourself. Check the crime stats, the local income and unemployment stats, visit the local police. The "sales people" who answer these ads are just fishing for business, they have no idea about economics and only want a quick sale. Be wary of these "professionals".
Also, be cognizant of the broader economic area and property market. In particular, the waterfront in downtown JC by Manhattan has seen a lot of growth in recent years. However, its a complete mess right now. Bear in mind, no local builders can get any loans, banks are lending and therefore the "development" stage is over for some time. I'm an international real estate investor and I've gotten burned in the NYC metro area. Bear in mind the Downtown Jersey City is flooded with unsold luxury condo properties. Most of these developers are about to cut prices dramatically -- which will have a knock on effect on all areas in the broader JC area, including Journal Square. Most of my hedge fund and private equity investor colleagues expect that the best parts of downtown Jersey City, eg. Paulus Hook, will "clear" when prices fall to around $250-320 per square foot. My guess is it will take until this time next year for that to happen. Also, a lot of investors like me are struggling to rent large inventories of units in the major luxury buildings. As I keep telling my clientele and investors "rents are falling, prices are falling, unemployment is rising..." don't be in a rush to buy. There will be interest to buy and redevelop these neighborhoods in coming years, but just not anywhere near current prices. Its not economical when banks won't lend and those that do are doing it at exorbitant interest rates. Builders in JC have been destroyed....