Perfectly good AFAIK - you end up using the same Apache2 server as Linux anyway and all the other usual suspects (PHP, Ruby, MySQL, node.js) are available. However, I'd only choose a Mac for server duties if I already had the Mac or needed the commercial iDevice management features in OS X server. You're paying a huge premium for the OS X GUI, and OS X Server is hardly a killer feature for web hosting: it makes the very basics of configuring web services nice and easy, but for anything more advanced you have to get into editing apache config files anyway, at which point you might as well be running Linux or FreeBSD.
However, what's your internet connection? Home/small business ISP packages aren't ideal for running servers - some ISPs actually prohibit running public servers, others make it difficult by not giving you a fixed IP. ADSL broadband connections are optimised for downloads and have pretty slow upload speeds (which is the speed visitors to your site will get). You'll need to leave your computer running and your connection up 24/7 and if you do create a successful site it will slow down your connection for everything else.
For anything other than experimentation I'd recommend using shared web hosting or getting a virtual private server - it will cost money, but so would getting a suitable, high-bandwidth internet connection! Usually these run Linux and offer a web-based front end such as Plesk or Cpanel for configuration: not as slick as OS X but fairly easy and more capable than the OSX Server GUI. There are companies that will lease you a Mac Mini hooked up to a decent Internet connection if you must.