Generally, I find that the font sizes used on many, if not most, web sites, are too damn small - especially on a 15" UXGA laptop screen. To avoid having to hit Ctrl-+ (text zoom) on every page I visited, I've been increasing the the minimum font size in the Firefox Options dialog. But this isn't an ideal solution - it screws up the layout of a lot of web sites. And minimum means minimum - you can't use Ctrl- - to zoom out and shrink the text size.
This week I ran across the NoSquint Firefox extension, which offers a much better solution. It allows you to specify a default zoom level used when pages load. Moreover, it can remember zoom levels per-site, so that sites with particularly sadistic designers can be set to zoom in more by default. It ROCKS!