1000x1000 pixels should be about max.
Not everyone is good with photos though, some are just starting out. Photo editing programs have a resizing function though and popular photo hosting sites have editing options if one doesn't own their own.
For example the pic below, I just now laid my S&W Model 29-2 down on my range bag and snapped a pic with my cell phone. I uploaded it to photobucket, cropped it, resized it and hit auto fix. Its not great, but considering it was with a cell phone, bad lighting, a bad background color and took less than 5 min, its okay. Its certainly better than if I had left it huge and unedited.