Some end of day spikes are attributable to short covering since some folks don't want to hold on to their positions overnight or over the weekend. If you're familiar enough with a stock (i.e. those you watch all day) you may be able to catch the bounce. Typically the stock gets puked out in the morning, beaten all day and just stays at the same price with high volume but there's a bunch of buyers in there too - you can see this with FTR this past Friday, which went from $3.92 to $4.00 by end of day (after hours). +$0.08 or +2%, you pick.
I'm not a shorter, but if a stock isn't down for any fundamental reason that I haven't been able to discern (i'm research intensive), it's usually a shorter. In those times I've caught it right, I've been lucky - not smart!