You may also want to play with the .SetLineCap and .SetLineJoin values for the context - these can make a difference, too.

Also, a lot of my older RC5 projects have the line cairo.FontOptions=CAIRO_ANTIALIAS_DEFAULT somewhere in them, immediately after instantiating Cairo. For reasons I never quite understood (given that I was, apparently, setting to its default value!), it seemed like I always needed that to get nice font rendering.

Perhaps Olaf would care to comment?