Suggestion: Place comments inside the font.xml file to indicate which font entry is used by which screen element. This obviates the trial-and-error method for those looking to change the size for specific elements.
Suggestion: Chosen font types should be tested for legibility as well as "clipping" (being truncated by too-small layout). On a 32" 4:3 NTSC TV, even the largest available font scale ("arial bigger"), have fonts too small to be seen in movie/music listings. At the same time, the fonts chosen were too large for the Weather screen, resulting in clipping.
Overall, the fonts and layouts look to be emphasized for HDTVs, and regular CRT TVs suffer for legibility, because of too-dense layouts and small-size fonts. Would suggest an optional low-density layout with large-size fonts, that stop short of clipping.
In an ideal world we'd love to have everything tested fully but since there are only so many of us working on this we can't test every single resolution and screen size along with every possible font option (never mind all the various views, options and other settings).
Therefore we test as much as we can and then rely on user feedback to tell us if there are any issues and then we try to fix them as best as possible.
I think you'll find there are more font options (3 different fonts and various different size options) than almost any other skin. Additionally this is one of the few newer skins that aim to support 4x3 and xbox users as most skins are targeted squarely at 720p.
To be honest, after the troubles we've had trying to support all these various configurations we'll probably be going down the 720p route for the next skin too.
My suggestions are about usability, which doesn't require more resource, but a simply a focus on the KISS philosophy. Up to now, XBMC has been in the techie realm. Now that it's expanding to different platforms, more regular users are trying it out, and they shouldn't have to suffer too much. Like my Mom.
Why not keep it simple and use a single font w/ bold & italic variations? Arial is pretty good for most everything. I noticed the other fonts used in Mediastream are structurally similar to Arial. Other skins don't seem to suffer with only one font, and it certainly cuts down on your resource cost.
As for the number of different outputs, there are only two ARs, 4:3 and 16:9. Legibility test is simply placing yourself at the normal viewing distance (6 to 12 feet) away from the screen, and see if you have to squint to read the onscreen text. Some of the listing options, such as the Info List, are simply not usable unless you have a 100' screen, HDTV notwithstanding, or you are sitting right next to it as a regular computer monitor.
Other usability issues stand out. One is inconsistent menu navigation, some of which are XBMC's problem, and some are Mediastream's own doing. The way the System Configuration menu is done is just horrendous, with "parent" options both to the top and the right side, and then there's the expanding/collapsing menus, depending on where the focus is. It actually took me a good 15-20 mins to figure out how to configure Mediastream. Being different may be cool, but simple is good.
These are meant to be constructive criticism. That said, I don't expect things to change for the simpler. I understand that's just the way it is.