PUG rules: Random grouping with folks outside the guild (referred to commonly as PUGging) for instances is fine, since we all have to do it some time or another. If you choose to PUG a raid, please respect your fellow guildmates and the infrastructure we have built for them. Please refrain from commentary about or linking gear in guild chat.
If you find yourself running with the same guild over and over again, please don't use us as a placeholder for your awesomeness. Splitting your resources between us and another guild or group is bad for both and beneficial for neither. Do what is right and move on to greener pastures.