I've been on WP.com for a few years now and when I started, I used to have the following problem all the time, then from one day to the next, it would fix itself. Anyways, it's been a very long time since I've had a spacing issue but it's back again (for me, at least) on one of my newly-made pages. I'm using the latest Firefox on Mac OS 10.6, btw.
So when all of you, who have made spacing problem topics here, just can't seem to get the spacing to work (by pressing return, shift-return or even doing it via HTML code), whether it be double-spacing or paragraphs, I made a simple workaround. Take a screenshot or find a small blank white image (depending on the color of your background) and insert it into the area you wish was spaced properly. Works like a charm. Oh, and you'll probably want to erase the link to that blank image in the image editor so that it's not clickable once published.
The blog I need help with is braztech.wordpress.com.