As noted in a number of places, this is great news on the SBLGNT site! I am grateful we have a new critical edition (of sorts) of the GNT. I am grateful that is free. I am grateful that Logos has worked with the SBL to make this possible, that one version of it can be integrated into Logos (cf. below), and other versions of it are or will be available in Logos' iPhone app, at the online Biblia.com site, and as XML and TXT files which means that other Bible software programs will be able to integrate it as well. [UPDATE: As Michael Hanel notes in the comments, it's already been ported to BibleWorks.] I am also grateful that we finally have a critical Greek text like this that is free from the hegemony of the German Bible Society! Yes, I will continue to consult my Nestle-Aland, but now I have a reasonable alternative that will alert me to points of divergences in the Greek text that are worth considering.
You will want to read the introduction to this edition, but basically what the editor Michael Holmes has done is started with the Westcott & Hort text and compared it to Tregelles' GNT, the reconstructed Greek text upon which was used by the NIV translation committee (edition by Goodrich and Lukaszewski), and the Byzantine text as compiled by Robinson and Pierpont. This approach does give preference to the Alexandrian tradition, but Holmes ultimately makes his own decisions. Holmes is not, therefore, working directly with the Greek manuscripts, but he is looking over the shoulder of these various text critics and editors and trying to make the best sense of all their direct research.
I was able to incorporate the text into my Logos4 program by following the download link, ordering it, and then starting Logos4 which immediately made it available to me. As you can see in the screen capture below, I can have quick access to the easily understandable apparatus (something that cannot necessarily be said of NA apparatus), and I do still have my NA27 at the ready. For example, from this shot of Mark 1.1, you can see that Holmes has chosen as the best reading to omit the υἱοῦ θεοῦ, but the apparatus indicates that he is following Westcott & Hort in doing so but that the inclusion is supported by the other Greek editions.
So head on over to the SBLGNT site, check out the resources there, and download this text in whatever format works best for you.