True life example: I live in East Palo Alto (EPA), and have lived there a little over a year. After my landlord in [city near EPA] started raising my rent by $100 every other month circa 2008 - 2009, I could not afford to live there any more. I moved to the least expensive place I could find, which was a garage on California St. in Mountain View that someone had converted to a rent dwelling. After moving in, I discovered that it was literally infested with black widow spiders and other creepy crawlies -- nightmarish. I couldn't live there.
I drifted for a bit, and eventually ended up renting a room in a shared apartment, from a lady with a condo and a mortgage in Mountain View. After a short while, she figured out with just a little bit more money from me, she wouldn't have to work full time, and therefore decided it was me who should be paying the bulk of her mortgage. So she raised my rent little by little, and when I protested because I didn't have the cash (I was working at a coffee shop at the time), she said "Why don't you just get another job at Carl's Jr?".
Most landlords have a similar attitude: modern day slavery.
When our room rental price negotiations fell apart, she called the police who literally escorted me onto the street. Thank goodness for the kindness of a few HackerDojo people, or I would have had to go to a homeless shelter. Mind you, this all happened while I was employed, working as many hours as they'd give me, in the city where I lived. I don't see any basis for the argument that I should've moved where it would be "cheaper" to live. (I walked to work at the coffee shop because I had no vehicle at the time).
Cuban's education explosion article yesterday hit home -- yes, a fully competent person with a master's degree -- working at a coffee shop for just a smidgen more than minimum wage.
In early 2011 I moved to EPA, which does have rent control. A studio apartment was all I needed, and got into it for less than I'd been paying for the spider-infested garage in Mountain View circa 2009. The price was just a tiny bit more than I had been paying for the shared apartment in Mountain View and the studio was 10X nicer (and private).
At the end of 2011, I got a bunch of mail / notices that the company which had a monopoly on all the apartments in EPA had been bought out by a _bigger_, more ferocious anti rent-control monster known as Residential Equity. And the first thing they did was raise my rent by as much as they possibly could. Lucky me, the rent control laws in EPA mean that they can't raise my rent by as much as they want, (which I am sure they would LOVE to do with Facebook moving next door) as a means to kick me out and make room for the Facebookers with bulging bank accounts.
Without the rent control law, there would be nothing stopping the same thing that happened to me in [city near EPA] from happening all over again. Or to my friendly (albeit not the best at English) neighbors who tend to be employed in the hospitality and service industries.
With the takeover, my rent did go up by more than I'd like, but it didn't go up by more than I could afford.
So that, my friend, is the definition of "affordable" rent. It's not as distinct from rent control as people would like to think.