Updated: Please see click on comments below, where James responds with a very good point
A number of noted experts have started conversations on a similar topic, but from different angles recently; namely how well certain products fit, or could fit, in a web content management scenario.
Dan Keldsen of AIIM, started by asking a question on LinkedIn, ref use of Microsofts MOSS2007 or WSS (i.e. Sharepoint technologies) for external web sites. Although there are definately some good and 'large' sites out there, with many people responding to Dan's question with examples, there are others who note that Sharepoint is a platform, an that said platforms strongest point is not web content management.
In a similar vein Seth Gottlieb noted that the WCM scenario is not Alfresco's strong point, and James Robertson responded with a comment about Alfresco being one of the products with a 'document management' oriented viewpoint, and thats one reason why it may never be great at WCM.
Both Seth and James point to 'integration', so for example on the open source front Alfresco has integrations with Drupal and the Liferay portal, whilst on the MS front, I have recently been researching CMS's vendors who have MOSS or WSS integrations.
So it seems to me, that as is often the case in enterprise software, whilst 'platforms' might be a key piece of infrastructure in your enterprise architecture, you should not attempt to shove that square peg into the round hole just because your 'platform' vendor tells you round holes are a good thing ! Whilst the devil is always in the detail, and in some scenarios there will be benefits to limiting the proliferation of software, quite often it is about finding the right tool to do the right job, and ensure that everything fits together and plays together nicely. Which is a nice way to end with a pointer to Pie's latest piece on ECM standards...........