One note; if you want people to READ your page, rather than just admire your background, try to minimize the contrast and edges in your background and maximize the contrast between text and background. Smooth, low contrast backgrounds with type of very different value (that is, darkness or lightness) are much easier to read against. Your users will thank you.
Finally, the tile is saved as a JPEG, which is acceptable for a background. In order to make the JPEG as small as possible I save at the lowest possible quality. This minimizes the time that a user has to wait for your background to download before they can read the text of your page. Don't forget they're not there to look at your background!