I think it looks much better (particularly on the islands). Cartographist has a point when he says that left unimpeded by man, forests will just stretch on in unbroken swathes. I remember wondering what to do about very large clearings that the mask made (you've got one in the NW of the large continent) so I stuck a town in the middle of it to account for the clearing. Where there were long strands of forest, I put in rivers to follow the strand so it made it look more believable. So basically, you use man or natural objects to explain any wierdness of distribution!
Re the tapering lines, the vector app I use has a ' pen pressure simulation' setting which allows you to make tapering lines, although I don't know if Inkscape or Gimp support this.