Career Change - Building a Portfolio Advice

So someone posted previously that they were attempting to make a significant industry change into Ruby On Rails and I’m doing the same thing.

I realize one of the most important things in getting a job in ROR or Ruby is a portfolio demonstrating what you can do. I’m wondering if people have suggestions for some ‘small’ portfolio building type projects. I have many ideas but they are kind of huge engrossed projects that I still need to think out. I have one small opportunity as a co-worker has a photo upload site he has for mountain climbing that is pretty primitive (and allows me to work out my first ‘non hartl tutorial’ gem in Paperclip) but I was wondering if any other people had any portfolio ideas that were things you could build on your own without needing a client?

I have done numerous web searches on the idea in the past and never came up with any quality search results.

My suggestion might seem a little different than most: following this
list, or reading over the problems people encounter over at stack
overflow, or other areas where people express the problems they're
having, use those problems as your own koans on how to work out how to
do those things. They can just be small, expressive examples of how
you go about implementing a bit of functionality in Rails. You might
even then be able to use them as examples to help others, and build
some good will and demonstrate your abilities.