Pros:
- They actually work quite well for all but about 2 weeks a year, when it is just too hot and muggy for them to be effective.
- Very easy to maintain, but you do have to do the setup in spring and takedown in fall.
- Location is important. I hope it's not a window-mounted cooler in some room. Ours was roof-mounted, with the blower in a central part of the house.
- Summer utilities are a lot cheaper than A/C
- having all your windows open all summer. I loved this, and miss it now that we have A/C.

Cons:
- setup/takedown. If it's on the roof, you're getting up there a couple times a year just for the swamp cooler.
- They're loud
- if you have a piano, it will go out of tune a lot
- I suppose you can set it up to turn on/off with a thermostat, but I suspect it will just have to be manually on/off (like ours was)