Myself and an associate are looking at doing a huge database system, the closest equivalent would the TradeMe I guess.
He is the PHP programmer, I am a programmer from way back, but with little PHP experience.
My thoughts were his expertise for his designed core modules, integrated with Silverstripe, and with me familiarising myself to Silverstripe or similar CMS so that we can both maintain the system functions more easily. Any comments please?

I have read the following:
When not to use a CMS
Just as it is important to choose the right content management system, it is also important to know when not to use a content management system.

We have seen projects where people have done things using a content management system which should have never been done in a content management system, and which should have been done using custom code.

Publishing flexible content is done very well in a content management system. Transactional Processing such as accounting, Customer Relationship Management, ERP type systems – things which are highly structured, maybe should be managed using some other type of application or even custom code.

We add this caution because we have seen customers and developers alike try to use content management systems for things which they where never designed to handle. In the end they ended up with expensive projects which don’t scale, or which can never help the customer reach their end objective.

Thanks Tama we actually have a PHP auction site installed, but this will likely not suit our needs due to the need for others to maintain it. Thats why I was asking the question about CMS and if using CMS eg Silverstripe would be a viable and robust method given the prospective size of database. I guess you answer the question by confirming that TradeMe use CMS.
Xataface (mentioned in Geekzone) does look interesting, will need to look into it more.