Block corners are distorted when using pdflatex and flash-based pdf viewer
Slides made with beamer+pdlatex and viewed with any flash-based pdf-reader (in Slideshare, Scribd etc.) will show some clutter in the corners of the blocks (alertblock, exampleblock etc.).
If you look the slide number two here: http://www.slideshare.net/linjaaho/latex-and-slidesharefinnishfinal-7275984
you see the problem. By downloading the pdf and opening it with Adobe Reader you see no distorted elements.
There is a detour: if you use latex+dvips+ps2pdf, the problem disappears. The problem is probably related to embedding fonts in the pdf file, but I have not been able to investigate it deeper.
Finally, I'm not sure if the real bug is in Adobe Flash or in Beamer.