The opinion one will form of a product will be different along the life of the product. Let's take the example of software.

When you do the first installation, everything is fresh and it feels like the system work perfectly. Once you upgrade (to a new version, for example), you will see the full measure of the product's quality. When upgrading to a new version, the process should be smooth. I am not talking here about an absence of bugs in the system. What I mean is that the system should be able to take the previous version's data (configuration, preferences, etc), and fit them in the new system.

If that process is not smooth – as happened with one of the tools we use at Websystems – you loose the trust of your customers, and they will prefer to stick with the version they have, even if the upgrade brings more usability. If the hassle of the upgrade is too much, there will be an impact on subsequent sales to existing customers.