The great Evagrius Ponticus describes the struggle with this most dangerous passion:
The demon of acedia, also called the noonday demon, [see Psalm 91:6] is the most oppressive of all the demons. He attacks the monk towards the fourth hour and besieges the soul until the eighth hour. He begins by giving the impression that the sun is hardly moving, or not moving at all, and that the day has at least forty hours. After this, he continually draws the monk to his window; he forces him to go out of his cell to look at the sun and calculate how much time still separates him from the ninth hour (the hour of Vespers and the meal), and finally to look about here and there to see if some brother is not coming to see him...
This resonates very much with my own experience of struggles with this particular passion. The beginning of the attack of acedia comes as an invitation to divert one's attention from the prayer, work, or charity at hand and to pay attention to something else, which might be entirely innocent or even useful in itself. This is what Evagrius is talking about when he says that acedia urges the monk to look at the window to see if anything is going on, and finally to gaze about to see if anyone is coming to visit him.
It's very easy to let one's web browser become one of Evagrius's windows out of the cell. Even though I know that there are prayers to be made, things to do, people and projects to look after and books to read, something inside suggests that it would be good to open up some Firefox tabs and check the tropical storm activity out in the Atlantic one more time, check for Roman-Seraphic liturgical books on Ebay, or read another Wikipedia article about some entirely random topic, like the history of Dr. Pepper, the Gregorian calendar reform, or the geology of the moon.
Then, just as Evagrius outlines, the next thing you know is that you find yourself distracted and spiritually dissipated. And if you're anything like me, it's difficult to get a day back on track once this happens. This is why acedia has to be discerned quickly through a practice of vigilant guard of the heart, so that it may be cut off at its seemingly innocent beginning.