One swallow doesn't make a summer is the version I'm familiar with. A quick google, however, traces it back to Aristotle's Nicomachean Ethics:

[16] Moreover, to be happy takes a complete lifetime; for one swallow does not make spring, nor does one fine day; and similarly one day or a brief period of happinessdoes not make a man supremely blessed5 and happy.


http://www.perseus.tufts.edu/cgi-bin/ptext?lookup=Aristot.+Nic.+Eth.+1098a+1

I notice this translation:
http://www.mikrosapoplous.gr/aristotle/nicom1a.htm#I7 says But we must add 'in a complete life.' For one swallow does not make a summer, nor does one day; and so too one day, or a short time, does not make a man blessed and happy.

But the LSJ, is quite adamant that 'ear' means spring. http://makeashorterlink.com/?Z4E8217BC.

Of course, the difference between spring and summer may reflect the difference between the English and Greek climates.

Incidentally, how does one view the results of the poll? I voted but still can't see them.

Bingley