A tool is dead without a community of users, and a community of users is nonexistent without a body of work that can be studied and reused. Inkscape wouldn’t be quite as fun to use if you always had to start a project from an empty page, or if you had no one to share your work with.
The two main reasons to seek SVG art are learning and reusing. Reusing is simple; this is what the whole idea of “clipart” is about. Instead of drawing everything from scratch, you take elements created by someone else and combine them with your own stuff (only if the license for those elements permits that, of course).
When reusing others’ art, source format is not too important as long as Inkscape can read it (Appendix B). Not only SVG, but PDF and AI files[1] can be the source of vector images for your designs. PostScript and EPS (Encapsulated PostScript) are supported to a lesser extent. CDR (CorelDRAW) files can also be imported, and future versions are likely to support the XAR (Xara Xtreme) format as well.
Also, nothing prevents you from importing a bitmap file into Inkscape and either using it “as is” in your design, or taking advantage of Inkscape’s versatile bitmap tracer (18.8.2 The Trace Bitmap Dialog) to convert it to vector shapes.
Even if you don’t use clipart, learning is always a good reason to download the SVG source of an image you find interesting. Unlike a bitmap, a vector image contains a lot of information about the way it was created, and in Inkscape you can examine that information in detail. The correspondence between visible areas and objects, the types of these objects, their properties, grouping and layer structures—all these aspects are very instructive for anyone studying Inkscape or SVG techniques.
Inkscape’s files are easy to find online compared to most other vector tools. It shouldn’t be surprising given that its native format, SVG, is human-readable and naturally web friendly (it is directly supported by most recent browsers). Moreover, as open source software, Inkscape promotes a culture of sharing that extends to its graphics as well. There is tons of SVG content on the Web already (search Google for filetype:svg)—much more than AI, CDR, or XAR files (but still a far cry from Flash[2]).
Apart from searching the Web for SVG content, you might try the following resources:
Open Clip Art Library (http://www.openclipart.org) is a community site with a lot of public domain clipart in SVG format. Inkscape can even import art directly from and export directly to OCAL.
Wikimedia Commons (http://commons.wikimedia.org) contains thousands of SVG images of all sorts, most of them created in Inkscape.
InkscapeForum.com (http://inkscapeforum.com) and the Inkscape group at http://inkscape.deviantart.com are two of the places where Inkscape artists share and discuss their creations.
The Inkscape Wiki (http://wiki.inkscape.org/wiki/index.php/Galleries) contains a list of online galleries for individual artists.
[1] Only PDF-based AI files are supported, which means AI files saved in versions 9 or newer of Adobe Illustrator (B.6 AI (Import)).
[2] Ironically, these days Flash is more often used for video than for its original purpose—animated vector graphics.