To catch up and answer a few of the questions about the nature of angels from my perspective. I do not believe that everyone has an individual guardian angel. I believe in the biblical teachings about angels, namely that they are God's messengers and He can send them to deliver a message or help out in particular situations as needed. Whether these are very rare events or frequent ones where the angels just appear as a normal human to others and so aren't generally known about, I'm not sure. As I understand it from the biblical context and teaching, angels either appear as normal humans (so we wouldn't necessarily know whether and when they're with us), or else on very rare and special occasions (such as the birth of Christ), they appear in a very dramatic and radiant form, presumably deliberately to be known and recognised beyond doubt by the intended audience (eg. the shepherds).
So I don't believe that white feathers are angels, nor that they leave them as signs.
Of course, not all angels, or spirits, are good in my Christian understanding. And, of course, I'm sure a good percentage of claims about them are hoaxes, etc. But that's not to deny their reality from a Christian perspective as scripture does give some teachings about them.
For me, it would be very important to test any perceived message that someone said they had from an angel or other "spiritual" source against scripture. It is vital (for Chrisitians) to test and discern both hoax and evil messages from the truth as we understand it. One of the main tests for us is whether the message supports the nature of Jesus Christ as the Son of God, and does it convey the love, grace, mercy and redemption message as taught by Christ. If such a message failed these basic tests and went against any of them, then it can be instantly rejected as either hoax or bad, etc.
As I say, this is how I believe and understand angels and spirits in very basic terms as a Chrisitian. If anyone was interested in particular bits of scripture to understand where those understandings come from, I'd be happy to share that.
So, hopefully that covers my own understandings 