When i started working on SharePoint , i never thought it to be more than a document management system . Even today when i mention SharePoint i know what's in the end user mind( Document , Document , Document .......) .
SharePoint has changed so drastically within past decade. I was always excited about the fact that it's possible to develop custom application using SharePoint 2007 as base framework . We did multiple implementation and development time has reduced around 50 % . Reason is that we dont need to spend time doing too much data modelling obviously there is downside to it as complex data centric application is not real contender for such efforts and neither transaction based application . But what i have seen as per my experience is that in any organization there are very few key applications which are complex and they are mostly business drivers other are small custom applications just to automate business process and no surprise that these small applications sometimes makes more than 50% of the applications in an organizations and are good contender to be developed using SharePoint as framework .
Custom applications developed on top of SharePoint 2007 comes with drawbacks too , biggest evil is performance. Too much of data will drain the server resouces and might take ages to load pages. So i would say application development in SharePoint 2007 has proven to be more of POC and learning platform.
SharePoint 2010 seems to much more mature with its 64 bit architecture and promises to provide deliver better performance.
Story cut short , non business centric applications will be developed using SharePoint in future. So if you would like to equip yourself then refer the below URL :