Steve Hayes over at the Khanya blog has asked the question "What is a miracle?" and answered it in terms of his own Orthodox Christian faith.
I tend not to use the word miracle very often, but when I do, I tend to mean something like “signs and wonders” rather than a supernatural thing (as I don't believe in the supernatural).
I find Jung’s concept of synchronicity more useful – “the acausal connecting principle” – where two events that have no connection nevertheless occur at the same time, thereby creating an apparent connection.
One example of synchronicity that I have experienced was the day I gave an address on the subject of gay rights, and a gay couple came to the chapel for their first time at a Unitarian service. The reason this was synchronicity, to my mind, was that I had been asked to do the service (Palm Sunday) at the last minute, and was sitting and racking my brains, thinking, argh, what do I know about Palm Sunday? So I went to read the Gospel accounts of it, and it reminded me of the downfall of celebrities, and then of the arrest of Oscar Wilde at the Cadogan Hotel. So I did the service about LGBT rights, but it wasn't premeditated, nor was the topic advertised in advance.
And then there’s the question of the difference between miracles and magic. (I know that the difference is clear in the Christian paradigm, where miracles come from God and magic comes from human or possibly even diabolic agency; but others use the words differently.) I was interested to note that various Orthodox saints are called Wonderworker, Thaumaturgos in Greek, and thaumaturgy was a branch of magic in the 16th century. Miracles are considered to be performed through these saints by God; not by the agency of the saint (though presumably their holiness makes them a fit channel for the miraculous energy of God).
To my mind, magic is a little-understood natural power or a property of nature that can be deliberately wielded by humans (like telepathy, healing, etc.), whereas miracles are events not caused by humans that are still inexplicable and full of wonder. I don’t believe in the supernatural (being a pantheist), so if miracles and magic exist, their source must be inside nature and not beyond it.
Aleister Crowley's definition of magic was "changing consciousness in accordance with Will" (he was quite scientifically-minded really) and various Pagan and occult writers have since defined it similarly. So, in Pagan and occult thinking, magic is a deliberate procedure such as meditation, prayer, healing, visualisation, invocation, evocation and so on, which will result in a change in consciousness. Miracles don't really come into Pagan thought much at all.
Unitarians tend to think of miracles as pretty unlikely - we celebrate the miracle of Hanukkah with emphasis on the renewal of freedom of religion that it entailed, and we celebrate the miracle of Christmas with emphasis on the miraculousness of every birth and the divinity within everyone.
Unitarians do practice meditation, prayer and sometimes visualisation, but it's not referred to as magic. Perhaps just as well, since (for everyone except Pagans) the word is so loaded with connotations of wielding supernatural powers.
There is also a problem with the magical mindset, in that everything comes to be seen as a sign or a portent, even when it isn't. People have forgotten the need for discernment - trying to work out if the apparent omen is actually an omen, or whether it's just a passing phenomenon. This is why we need reason, and to balance open-mindedness and scepticism. I always try to find a natural explanation for something first, and only if one cannot readily be found would I accept it as something magical or miraculous.
Arthur C Clarke famously said, "Any sufficiently advanced technology is indistinguishable from magic." And Larry Niven and others have turned this around and said "Any sufficiently advanced magic is indistinguishable from technology." Either way, if science was less materialistic, it would undoubtedly be able to investigate and explain so-called magical phenomena. It has already been demonstrated that meditation works and is beneficial; why not other spiritual practices? There's nothing supernatural about these practices; they have demonstrable psychological and physical effects.