I stumbled across this site recently, which is a bit odd but also interesting.
It lets you create flash cards of kanji, as well as full sentences, and select voc from the sentences for your own personal flash card system. It claims to have 15,000 real japanese sentences.

However sentences seem to be a bit slapstick side, from the few I looked at.

Anyways, seems to be an interesting site to play with a bit, though not to sure how academically sound it is.

ファブリス, if you haven't seen it yet, you might have a look cause it seems to at least attempt to do what you are planning to with the update.

[ファブリス]

zazen666 Wrote:However sentences seem to be a bit slapstick side, from the few I looked at.

The sentences probably come from the Tanaka Corpus. It's only a guess because I know Jim Rose, author of the site, is on the EDICT mailing list where they discuss this collection of sentences in addition to the dictionary files.

There should be a big disclaimer and FAQ about the Tanaka Corpus on every site that uses it. I know it exists on Jim Breen's site, but that site isn't exactly a testament to design or accessibility.