what resolution i use depends entirely on the monitor itself. i used to have a 17" monitor at home and i kept that at 1024x768. now i have a 19" monitor at home and i keep it at 1280x1024. at work i have a 23" monitor and i keep it at 1600 x 1200. so yeah, i'm difficult.
i do think though that image size should be limited to either 600x480 or 800x600 for the sake of both pixel size and actual file size. there really is no need for HUGE pictures anyhow ya know...