There really isnt any need for multicore right now for desktop cpus, servers would need it definitely however.
What are u going to do? encode a dvd, copy a dvd and play 2 games at once? playing mp3 only needs a fraction of one cpu, same with voice communication.
I bet when FEAR comes out it says its optomised for dual core but i bet the difference between a amd 3700+ or fx-57 against dual core 3800+ would be only slightly faster, at most 20%. Cause it is really hard to properly program a game which utilises dual core fully, threads need to wait for other threads to finish to pass values/parameters that it needs.
Get the 3800+, dont wait to 2008.