The filter effect <feGaussianBlur> available in SVG specification (http://www.w3.org/TR/SVG/filters.html#feGaussianBlurElement) is often (or rather most of the time) not rendered correctly on all Wikimedia projects.
This is a known problem of librsvg (see https://bugzilla.gnome.org/show_bug.cgi?id=605875) but probably won't get fixed in the near future.
For some quite impressive examples refer to:
- http://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/VirtualDub_Logo.svg/195px-VirtualDub_Logo.svg.png vs. http://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/VirtualDub_Logo.svg/196px-VirtualDub_Logo.svg.png
- http://upload.wikimedia.org/wikipedia/commons/thumb/f/f6/Audacity_Logo.svg/127px-Audacity_Logo.svg.png vs http://upload.wikimedia.org/wikipedia/commons/thumb/f/f6/Audacity_Logo.svg/128px-Audacity_Logo.svg.png
This bug severely restricts the possibilities of graphic artist on Wikimedia projects since it basically renders the Gaussian blur filter completely useless since the final rendering of the MediaWiki software is rather arbitrary and comes near to gambling in the end. However Gaussian blurring is heavily used in modern SVG images since it allows to create outstanding effects like 3D effects and superior shading.
Besides art created exclusively for Wikimedia projects, many free SVG images from other sources can't be used either since they are just not compatible, would need a lot of work to render correctly at all and wouldn't look nice in the end anyway.
Therefore it would be badly needed to either change the SVG renderer (maybe only for problematic SVG files?) or to finally fix the bug in librsvg (maybe consider http://strategy.wikimedia.org/wiki/Proposal:librsvg_development_funding ?)