When donating to the giants, what is taken into account when determining the amount of favour I get for a donation? Is it anything other than monetary value of the items donated?
The amount of favor you obtain when donating is equivalent to its value listed on the item's info page divided by ten. The value seems to be rounded to the nearest whole number (.1-.4 will be rounded down, .5-.9 rounded up). This applies to all items you throw into shrine - all giants treat all items equally.
The only exception to this rule, as far as I know, is elements - even though they have no listed value, when donated they give a small amount of favor. One thousand red element for instance seem to yield 20 favor.
Using Shrine Powder will increase the value of your next donation. Fairly Hallowed Shrine Powder will double the value, while Extremely Hallowed Shrine Powder will triple the value. To farm favor efficiently, you should gather up a large number of one type of item and donate them all under the influence of Extremely Hallowed Shrine Powder.
The best resource on this topic is Zu's forum thread about giant donations, favor, and skill time reduction:
You may also want to check out my FavorSaver, which is an API app that helps you maximize your shrine donations.
It can read your inventory and let you sort through the items you have for donation, apply shrine powders, and view exact amounts of favor generated per item.
To answer your question directly, the amount of favor generated is equal to the currant (Glitch currancy) value of the item divided by 10.
You also gain XP for donations, which I am tracking and determining the formula here:
Although I bet Zu's post will be updated when we have some hard answers.