In his Opening Lanes column (permanent link here) today at ChessCafe, Gary Lane looks at some games with the Max Lange Gambit (a.k.a. Koltanowski or Rosentreter Variation of the Two Knights Defense or Giuoco Piano, which begins 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.O-O Nf6 5.d4). Most of his analysis follows Lev Gutman's excellent series of articles on the line and on the related Max Lange Attack in Kaissiber #22-27. As a firm believer in the Modern Horowitz Variation of the Max Lange, which Gutman endorses (with reference to my article and a picture of me, which was nice), I was pleased to see that Gutman's analysis is gaining a wider audience and wider acceptance, especially since the gambit with 4.O-O and 5.d4!? has long been in disrepute (despite some excellent discussion of it by Jude Acers).
I would not be surprised to see a general revival of this line, especially at the amateur level. One encouraging sign is that Mihail Marin's very recent and generally excellent Beating the Open Games recommends (in Chapter 8) that Black avoid the "risky" acceptance of the gambit pawn with 5...Bxd4 6.Nxd4 Nxd4 and instead transpose to the regular Max Lange Attack with 5....exd4 (which he calls "The most consistent answer"). If his recommendation begins to prevail, I may well make these lines more central to my repertoire, especially since his treatment of the Modern Horowitz Variation completely overlooks improvements mentioned in my piece and analyzed extensively by Gutman as being in White's favor.
You can read more about Gutman's analysis in Stefan Bücker's piece "The Magic of Move Orders." Or get a copy of his series of Kaissiber articles for yourself before they sell out.