Well, (unfortunately) I can say pretty confidently that nobody has played as much GSC as me over the past couple of months, and I'm certainly seeing both Vaporeon and Espeon used as much if not more than a few of the pokes already considered OU (Zam, Rhydon, Missy).
I don't really like putting the value on how commonly used it is, though. From a viability standpoint, Espeon and Vaporeon are both potent sweepers. In fact, with the word being out now on how good Vaporeon can be, plus hp legends making marowak less common and machamp more common, Espeon may be even better than Vaporeon right now. It's major advantage over Vaporeon is that it's a good BPer (Vap is pretty bad as a BPer imo) along with being able to beat down electrics instead of dance around them like Vap does. It's hard to really wall or stop Espeon without Lax (Roar ttar I guess?) unless you're going to eventually explode on it with something like egg or steelix. But in addition to the extra hurdle of dealing with Electrics, Vap can be walled pretty hard by some additional stuff that I'm seeing more commonly right now (Egg, Suicune).