The Gospel of Judas gets a good deal of action in academic circles devoted to the study of ancient Christianity, as /u/anoldhope mentions. (Take a look around JSTOR or Google Scholar, for instance.) In fact, it gets just as much scholarly attention as any of the many other ancient, non-canonical gospels.

As for GosJudas' lack of "impact" in modern religious practice, that depends on several factors. (N.B.: I am a Christianity scholar, so I will limit my discussion to modern Christianity.)

In Christianity, the focus has historically been placed on the canonical New Testament, and any books outside that canon were treated with scorn and condemnation.

Many modern Christians (specifically those from conservative traditions) maintain the same scorn towards these other Christian texts. Other modern Christians (usually, those who are more progressive) do not actually feel any animosity towards ancient, non-canonical Christian literature, but still neglect it, because of the longstanding focus on the canonical NT. Finally, a somewhat smaller portion of modern Christianity actively embraces non-canonical literature (as exemplified by the New New Testament.)

Further reading:

-On the varieties of ancient Christianity, see Bart Ehrman's books Lost Christianities and Lost Scriptures.

-For a conservative Christian reaction to the Gospel of Judas, which typifies the tradition's views on non-canonical gospels in general, see Albert Mohler's blog post, "From Traitor to Hero? Responding to 'The Gospel of Judas.'"

EDIT: Fixed a typo.

Scholars still study it. In fact, I gave a paper (partially) on it at an academic conference not much more than a year ago. :P

I think it probably has made a bigger impact than you'd think. The general public tends to be pretty gullible to sensationalism - of the Dan Brown variety or whatever. I'd imagine some non-Christians (and New Age-y types who see some "spiritual" truth in Christianity) probably have some notion that this is a text which is a viable alternate to the "orthodox" gospels...and they may think that Big Bad Orthodoxy suppressed it (for theological/political motives or whatever). In other words, they may have some idea that this gospel represents a "truth" on the same level as (or perhaps higher than!) the one that the other canonical gospels do.

It's certainly made less of an impact among conservative Christians. I suspect that once these people have some notion that this represents a challenge to their beliefs that needs to be confronted, they'll investigate the context in which this gospel emerged and - well - discover the context.

(I guess I should say that I'm an atheist/antitheist - I'm just trying to delve into the psychology and sociology of its reception.)

Basically, people who look into the context of GJudas will find that it's a product of a particularly idiosyncratic Christian tradition that was quite far removed (temporally, ideologically, geographically, etc.) from the circles that wrote the earliest canonical gospels. Hell, the extant fragments of Judas aren't even in the same language as the NT (although many these Coptic texts are hypothesized to be translations of Greek originals).

One last note: even though this gospel may be thought of by some as a "competitor" to orthodox Christianity, when you actually think about it, there are obvious major elements here that represent a sort of apologetics for a strand of "orthodox" Christianity, in a way. As opposed to the (potential) embarrassment of the Messiah himself being betrayed by one of his own disciples, instead, in GJudas, you find the idea that this was Jesus' plan all along.

You may also want to post this question in/r/AcademicBiblical/