Someone from Distil networks posted a series of scraper test drives using various tools and techniques against their technology.
Scrape Bot Protection Test:
You can obviously use their testing methodologies to validate your protection against bots.
It's possible you find holes in your methods and either decide to switch to a service like theirs or get a better script for your own hosting.
Scraping through a CAPTCHA:
Couple of other related scraper testing posts also worth a read.
I found it interesting to say the least ;)
DISCLOSURE: I'm not related to or have any personal interest in the site, service or links posted as it's presented here strictly for educational purposes.