Ajax, jQuery, JSONP (JSON with Padding) & YQL make a heady combination - check Christian Heilmann's code samples.
Some facts about YQL from around the Web (work in progress) -
* YQL is a hosted web service that can scrape HTML for you. It also runs the HTML through HTML Tidy and caches it for you.
* It only returns the body content of the HTML - so no styling (other than inline styles) will get through.
* ...it treats the info on the web as a virtual table that developers can manipulate in a standardized way, regardless of the API that data came from.
* YQL understands and supports data sources like RSS, Atom, JSON, XML, CSV, HTML, Flickr, Yahoo! Finance, Weather, and so on.
* ...makes client-side mashups possible without using server-side proxies.
* Usage Limits:
Per application limit (identified by your Access Key): 100,000 calls per day
Per IP limits: /v1/public/*: 1,000 calls per hour; /v1/yql/*: 10,000 calls per hour
Also see:
HOW TO prevent screen scraping
Google Spreadsheets functions for scraping external data
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