In several areas there are excellent open source solutions. Two of these areas are Network /Host / Service Monitoring and Intrusion Detection (IDS). We are using Nagios for Network Monitoring, and its very powerful. It does a number of things we could not have done with proprietary monitoring software like WhatUp Gold or ipMonitor.
However, the amount of time it took to get it up and running, to customize it, add required 3rd party modules etc was enormous - two man months at least. And you need at least 2 or 3 admins who acquire the required knowledge.
For a small IT department with just 2-3 network admins running a complex network with around 50 servers, 3 man months is a big investment of time, because usually besides daily work they can spend just a few hours a day on doing something new.
Economically, this makes the most sense if the acquired knowledge and experience can be applied several times, i.e. for several networks. This is why I chose the headline "Open Source Software can lead to outsourcing".
Commercial software vendors make a significant investment into "productizing" their software solution, i.e. documentation, streamlined setup process for quick deployment, wizards etc. With open source software, this is missing and instead of paying for the license you have to pay for the specialist to get the solution quickly up and running. Of course you can also do it yourself, but that is even more expensive except if your labour cost is very low or if you are a very large organization where you can reuse the acquired knowledge many times. This might be an explanation why open source software is so popular in developing countries, universities, government institutions, and non-profit sectors in general. On the other side, ASP is the logical evolution of commercial packaged software.