The Web, as a delivery mechanism for transactions and data doesn t make these problems go away. The real challenge is getting your internal systems ready to work with electronic commerce and extranets to your trading partners. The web interface to these systems is the final testing phase. Limited rollouts need to test the server side applications and database transactions before ever going live. Once you are up and people are connected you will have a very hard time doing major architectural changes.
Systems held together by duct tape tend to blow up eventually.
An example of good planning is Dell Computers who spent a good 4 months just architecting their commerce solution while competitors were throwing out less strategic applications on the Web. Dell planned for huge growth before anyone ever saw their web site. Always test your server and database applications early. This gets most of the bugs out in the critical areas. Use a phased rollout and limit early exposure to get the bugs out.