More modern window A/C units sometimes have a timer on the panel. I think the idea is to set it to turn off after you've fallen asleep (and presumably it's cooler), or keep it cool for a while after you've left home and then eventually shut off on its own. See this model at Hammacher Schlemmer:http://www.hammacher.com/Product/81376?refsku=11636&xsp=1&promo=xsells
There are some nice (terribly expensive though, often twice as much as window units) movable units that vent out of a window rather than being mounted there:http://www.hammacher.com/Product/11636?refsku=81376&xsp=1&promo=xsells
While I don't think running it constantly is necessarily "wrong," these things do wear out eventually. I don't think it hurts to conserve the fan motor/bearings etc. a bit.
My bathroom vent fan motor just crapped out after probably decades of use, and it's something I have to replace (it's just a $15 or so motor I have to find at Lowe's). And I'm trying to live through this horrific heatwave with my central A/C at modest settings (80-81) because I just don't know how much life my 40+ year old unit has in it. The A/C repair folks in the past told me they just can't find basic replacements parts for it anymore.