This is such a deep topic. Lance, great job getting it going with some other thought processes. I like the "boots on the streets" approach to knowing your market. Take your smart phone, know your local online data source (portlandmaps.com for Portland) and go watch the activity. Go in side as many open houses as possible, look for dumpsters, research sales history, check out permit history for the renovations you find prior to them hitting the market, watch DOM, pay attention to the "players" in your market place, keep a very close eye on rents and retail prices, call all the FSBO signs you can, create your "drive for $" list, talk to locals, knock on some doors, drop off some door hangers.
When it comes to knowing your market you can get a lot online. All the stats and such, but when it comes to working the streets you can become intimate with your market and take those stats to a whole nother level. Of course this doesn't work well if you're investing out of area. The biggest reason I invest in my "back yard"
I also take "know your market" further to "know your buying pool". When you're looking at a specific opportunity...identify that retail "buying pool" and work backwards from there on your number crunching.