Our biggest challenge was finding people who understand the technologies and know-how to put it all together at internet speed. Not all the skills we need are easy to find. Finding people who are adept at setting up firewalls can be difficult too. In addition, it can be a challenge to find Oracle DBAs with the skills needed to set up a mission-critical database tuned for optimum performance. The lesson we learned is that if you want to build a highly scalable technology platform, you need to invest in enterprise skills from the start.
Some people try to take the simple route to setting up a site.
They buy a few NT boxes and an SQL server, and hire people with the associated skills. But when they try to scale, they find that they have to find personnel with enterprise skills, or retrain their team. It's easy to change boxes and software, but very hard to change the team. It's better and less disruptive to invest in those enterprise skills initially. This includes our task management, meeting management, calendar, and address book services.