The Google interface is truly a friend for us Dyslexics. Important text pops like it should through increased type size and color differentiation. Supporting information is set off from search results text in a color that de-emphasizes it (green vs. body black). Sponsored links are far off to the right, with a good deal of whitespace between them and your search results. In fact, the interface as a whole leverages whitespace very well. For the somewhat defective text-processing portions of my brain, all of this adherence to good page design practices is a godsend.
Then there's GMail. GMail seems to want to trash all of the rules that Google's search upholds. Whitespace is minimal. Body columns come and go (are you in your in-box, or looking at a message?), and you are swarmed with ancillary information top and bottom. Differentiation between important text and adjunct information is almost nonexistant -- the type is generally all the same size and face. Color differentiation is shot because almost everything is a clickable link.
The net result, for me, is a nearly paralyzing level of text-confusion. I can't read anything because it's all clamoring to be read with equal intensity. brianrogers sent me something lengthy today, and after thirty seconds of rising frustration trying to read it, I forwarded it to my regular mail account where I could read it with a text-only client (my beloved Pine).
GMail's Settings area is a unique island of sanity in this mass of clamoring characters. Its strong background color directs "look here"; the horizontal separators help section information off by task, and oh my God! there's whitespace! But that's really all the relief there is. Because, while the Settings area is well crafted, it doesn't actually allow you to change any of the look or feel of GMail that makes it so problematic.
It pains me to say this, but Microsoft apparently understands something about human beings that the GMail designers just don't. Microsoft's Outlook Web Access succeeds in supporting readability where GMail falls flat. The allowed customizations in OWA support changing typefaces, sizes and colors to meet the users' needs and preferences. I know, I know, OWA is a commercial product and Google Mail(beta) is a free service. But it's a free service that falls so far short of it's namesake free service.