Cross-Platform (Windows 32, All UNIXes, Mac OS (Classic and X))
The most complete browser todate in its support for standards. (some things are still missing, but work is carried forth in this direction)
Has many registered bugs, but they are relatively rarely encountered. (better than most other browsers, at least)
Still relatively under-used in comparison to MSIE. (at least on Windows, which is the most common platform)
Its developers made a conscious decision, not to support the MSIE deviations and extensions from the W3C standards, and so it often breaks in sites that only work in MSIE.
Verdict
Make sure your site supports this browser.
It is available on your development platform of choice, and many people use it.