GutenPrint 5.0 rc 1 produces text output on Epson C84, HP DJ5550, and HP PSC1350 which is as good or superior to that produced by the drivers provided by the vendors. The smaller the font, the better the output compares. Testing included text from Safari, TextEdit, Pages, MS Word, Graphic Converter, Photoshop, InDesign, Illustrator, Adobe Acrobat, Adobe Reader, Preview, and, via Classic and Apple's LW8 driver in Classic, Word Perfect 3.5e and QuarkXpress 5.0. Font sizes which are unreadable using the vendor drivers show clearly using GutenPrint. Fonts tested include Geneva, Arial, Helvetica, Times New Roman, Palatino, Optima, Tahoma, Tekton, and Belwe. Font sizes tested went down to 3 point. (Geneva 3-point is hard to read without a magnifying glass; with a magnifying glass, vendor driver output is difficult to make out. GutenPrint output is clear.)
GutenPrint produced far superior graphics output to that of graphics output produced by vendor drivers, with the exception of graphics printed from MS Word, where the results were the outputs were identically poor, suggesting that the problem lies with MS Word. Colour and grayscale output from Graphic Converter, Photoshop, Illustrator, InDesign, MS Word, Acrobat, and Preview, using .DOC, .GIF, .TIF, .PNG, .PDF, and .JPG formats (not all applications could use all formats) was tested. All test files had text, all had hairlines, all (except the .GIF) had gradients, all had photorealistic and hand-drawn elements. (I combined several pictures from Google's Test Picture site.) The pictures were converted to various formats using Graphic Converter, except the .DOC, which was a .JPG imported to Word using MS's picture import feature.
GutenPrint is now faster than GIMP-Print had been. The lowest-quality GP output is as good as standard-quality Epson and HP output and is delivered faster. Standard quality GP is between standard and high quality HP and Epson output. It is delivered slower than standard quality vendor driver output, but faster than high quality. High quality GP output is very slow, much slower than high-quality vendor output. It is also superior to high-quality vendor output. You can tweak GP printing further by going to and changing settings. If you don't know what you're doing you may get unexpected results.
In short, GutenPrint is at least very good if you print mostly text, and is vastly superior if you print graphics.