One of the most interesting take-a-ways from this deal is despite the over-all "lagging" commercial market noted in the Journal, the story suggests players are willing to pay top dollar for proven location (be it for branding or for leasing). Google had real business, and possibly emotional, reasons for this purchase.
When buying or selling residential real estate in Chicago, buyers and sellers are making very specific decisions based on monetary investment, location, emotion and timing. So, regardless if the national or city-wide market looks up or down, your residential property value is a moving target. The players involved will determine value as much as the the raw comparable market data. Especially if the player is Google.