Hi Julian....I put off entering mine in until yesterday as I really couldn't face the prospect of having to look them all up again and get the exact LDS references for them all....but actually in the end it turned out not to be such a huge job after all...
It isn't as onerous as it used to be. They've set it up nicely so that for large families it's only a few keystrokes more than the name itself - once you've got the head of household entered.
I think Lost Cousins is a brilliant idea - but I guess people are put off by the slog of entering stuff.
What's for sure, you're more likely to get contacts from people who are taking FH research seriously, in contrast to another site (now connected to a TV company)

JULIAN