for posting photos on the web for my personal use I generally keep mine small for several reasons.
1. Bandwidth , Im dial up friendly for the most part.
2. image theft. NEVER put full size high resolution images on the web for anyone to see, especially public browseable sites that any joe blow can stumble upon. Next thing you know you will see one of your images on a greeting card or in a magazine

with my name eating up the credits

and you will be all

now that I have tons-o-storage on my web host server I have upped my image size to 800x??? this is typically large enough for the general masses
just my own .02