if the agent had been correct (50% in account and 50% purchased) everyone on the other thread would have confirmed that is indeed the case. no one did. so it is safe to assume an agent misunderstanding.
appreciate it is you first booking, and many people think this is all too easy or too good to be true. but many tens of thousands of these are issued to millions of members worldwide every year. it really is a straight forward process... get the miles, jump on line, select the flights, pay the taxes and off you go
the only difficulty comes with availability at peak times, but if you are flexible you will generally have a good selection of flights. you don't need any miles at all in your united account to search for availability, so you can have a look at what's out there right now.
airlines make good money out of selling miles, so it doesn't really fit into the 'too good to be true' category as far as they're concerned. award seats are seats that would be empty anyway, and selling miles to passengers for 1.5c each beats them selling to banks and credit card companies for 1c each. they're making good money off these sales!