What does mast rake do?

really low windspeed=near as dammit nothing?

because if thats the case im going backwards anyway because of the tide.

you have got it sorted.  substantial differences between types of rig means that most of the above rake comments could easily be misinterpreted and applied to the wrong boat.

similarly you might want to flatten your sails in light winds as your sails are very full (eg you have an unstayed rig eg Europe/OK) and the wind will not have enough energy to get around a full sail.

you need to make the original question more class or at least type of rig generic as this will be key to understanding.  Best of all discuss with your sailmaker.  I realise that if you have SMOD sails made in the Philippines or similar this is a useless piece of advice but if that is the case it probably means you just have to look at what the fastest people in the Class do / ask them as you can surely have no alternative but to do the same.

Sorry, I tend to disagree, the flat sails stall quicker as the flow de-attaches quicker where as with the curved sail, the flow will follow the shape of the sail better. 1/10th camber seems the optimum setting according to some texts for light conditions. 1/20th camber produces less lift according to research but has a relatively similar drag profile, indicating that you get less lift for comparible drag. 1/7th camber, a fuller profile than 1/10th sees more lift but also has the penalty of more drag. If you put a flat plate into a wind tunnel, it stalls quite rapidly, the curved foil maintains a lift profile quite convincingly in comparison. Increasing the flow of wind through the tunnel, ie increasing wind speed helps at higher speeds to maintain a flow over the flatter sections, so flat sails don't help at all in light winds, has the same effect as oversheeting the main in essence.

(Camber is the ratio of sail length to depth)

So you think opening the jib leech by easing the sheet stops you pointing but opening it by raking the mast doesn't. Why? 

Most classes do in fact ease the jib-sheet at some point as the breeze builds. Some keelboat classes have tuning guides telling you how far the leech should be off the spreaders and these typically call for the sheet to be eased slightly in stronger winds.