Hi Adrian,
I have integrated indextank with ExpressionEngine, though there's not much especially EE-specific that needed to be done.
Basically, I have a script that retrieves all my content from the EE database and then adds it to an indextank index.
Then there's another script that lives in an EE plugin that handles the search results page in EE. It's a single function that passes the query string to the indextank php apiclient class, retrieves the results, and formats the output into nice search results.
It's been a few months since you posted, but if you're still interested in details just let me know.
Ian