While there is some definite appeal to iScript, there aren't many compelling reasons to use it instead of Perl or Tcl. Every aspect of iServer can be administered in this fashion, while detailed log files help track usage levels and site problems. However, there are some failings in iServer that will cause you to pause before implementing it on the enterprise level, scalability aside.
Security is subpar when compared to other enterprise-level Web server or application servers.
If you're willing to evolve your own system as iServer evolves, then it makes for an attractive tool. But if your needs are of a more immediate nature, you'll want to look at a more mature application server or Web server.