One thing i've always had to consider is what servers actually support Ruby. A few personal projects i've made in Ruby. However, when working on Web applications for other people (Who already have a server), they may not support Ruby (Or PHP for that matter).
I think it really comes down to preference. I learnt PHP first off, then discovered the power of Ruby.
Yes, initial marketing would normally look for a target audience (Not just on the internet - get on the phone too). Spend some time on forums, blogs, etc.
Find websites that allow you to write about your product(s) (What it is, why people should use it, etc).
Maybe even getting in contact with tech-based magazines. Ask if they can do a review of your products (Or hell, even feature the product/link to the product on a cover CD if they have one).
Marketing, marketing, marketing. Become a 'sponsor' of other companies, and look for a target audience. Just do anything you can to make people aware of your product.
Start sending emails, get on the phone. When you find people, give them a reason to use the product you're trying to sell.
I think it really comes down to preference. I learnt PHP first off, then discovered the power of Ruby.
I suggest taking a look at this: http://www.killersites.com/blog/2006/php-vs-ruby/