Using previous employment as a portfolio

Hi,
Im posting this as a follow up to the original thread regarding building a portfolio for interviews.
How about using past projects in previous places of employment as examples?
I think the problem here is one of disclosure and copyright. Obviously you cant take the source code that you wrote whilst working for a previous company and say "Hey, I wrote this".
At the same time it seems permissible to put on your CV "Whilst working for company X I worked on project Y that involved using tools A, API B and Database C"
Is it then permissible to make a diagram of said project to put across your point better? If so, could you use this diagram to add to your portfolio.
It seems that there is a very fine line to tread.
Best Regards,
Mark

I had an interview (some 4 years ago now) where the guy asked me to draw the UML class diagram of a project I had worked on (to some detail). I guess it could have been seen as a copywrite infringement, taking documentation however is not a good path to go down.

Generally describing past projects is acceptable. EVen draw general diagrams. The only time I'd be careful of doing this is if the design is some proprietary technology, or if you're talking to a competitor.
--Mark