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Transferring big files, at least with these free services, is iffy at best
TranferBigFiles' free iPhone app lets you upload and send video and photo files directly from the device without compressing or converting them first.
A review of the postings on this blog
Some successes, mostly failures.
SendThisFile competes well with YouSendIt and Box.net for sending large files that are too big to be e-mailed.