In fact, the install instructions are here: http://www.macspice.com/Installation.html. You will need to spend about an hour working through a couple of the tutorials.
MacSpice has several thousand users and there are no reported bugs affecting the current version (2.10.29). In the event that MacSpice crashes, it asks permission to report the crash back to me. Version 2.10.29 was released in December 2011, has been downloaded about 5000 times, and no crash reports have been received to date. Historically, the median time to diagnose and cure in response to a crash report is 48 hours, and and less serious bugs are typically fixed within 7 days of being reported.
As far as the disclaimer is concerned it is merely making explicit what is always the case with non-trivial software that is distributed gratis.