I have my consolefont set to a 8x8 font size. When I start the X server, the console font get double spaced, but it's more like there are two copies of each line, one overlapping the other. If I go back to a 8x16 font, everything is fine. I've tried setting the font size with both the CONSOLEFONT variable and kernel argument. I have to reboot to get the console back to normal.
This isn't the first time I've seen this, but both times have been on laptops. I'm currently using Gentoo 2005.0 on a Dell Latitude D505, but it happened to me on Slackware 9 a while back on an older Dell laptop.