Portable air conditioners: yeah or nay?

Portable A/C units are pretty much your only option if you aren't willing to/unable to get a window unit. The most important thing I would say is to figure out how many BTUs of power you need from a unit. The main factor in determining this is calculating how many square feet the area to be cooled is, followed by secondary factors such as how much sunlight the area gets, if a kitchen is in the area, and how many people will occupy the area at any time.

Here's a decent guide from Lowes
http://www.lowes.com/lowes/lkn?action=howTo&p=BuyGuide/AirConditioner.html

As for portable AC units themselves, having used one, I would say they are basically a fan that blows cold air. They can keep a room at a decent temperature during a normal day in the high 70s/80s, but once a heatwave hits, it really can't handle it. They can get the job done for a small bedroom so if you're sharing an apt with roommates, you can keep your room comfortable with a portable unit.

Also remember you don't want to go overboard on the BTUs, get too powerful a unit, and it won't properly dehumidify the room making it very uncomfortable.

Hope all that helps!

Those things look like massive energy guzzlers, and don't you have to stick a hose out a window or something on them?

I wonder if cooling down a difficult room could be just done with one or two really good Vornado fans....

the problem is that when you stick a portable AC in a small enough room - all the cooling is undone by the excessive heat from the unit itself. its SUCH a bad idea unless you really have no other option.