I have more than 20 filters, how can I easily reorder them?
GMail natively does not have this feature. However, there is a Filter Import/Export feature in the labs that you could use, though it involves editing xml.
Once you enable the feature and Save Changes, go to Settings > Filters.
This will result in an xml file. You could edit the xml file to move the order of the filters, and then reverse the process and import them.
Any time you save a filter, it goes to the bottom of the list. Once you know what order you want your filters in, open each one in order, and just click Save without changing anything. When you get to the last one, the filters are all in order.
Of course, you would have to repeat this if you ever really did have to change a filter.