Well, since I work at a shop that sell Cannondales and there are 3 Cannondale bikes in my garage, I can say that Cannondales makes great bike w/o a doubt.
But, you pay the price for it! The old, "You get what you pay for!" statement comes to mind.
The biggest problem I see here is that Giantismic is looking for a decent bike for around $750-$800. Well, MSRP on a F400 is around $900. So, that puts C'dales out of the question anyways.
Also, he's a 19 year old kid/young man, who doesn't want or need the BEST, just something to get started.
If I were to compare side by side the Rainier and the F400, hands down I'd choose the Rainier for this type of rider.
Now, IMO, Giantismic,
Does this bike allow for decent size impacts and fairly rough trails? My firends rides single track trails all the time, so would this bike perform well on them?
from your description, and knowing how a 19 year old is going to be more abusive, I would recommend more of a "Freeride" bike.
The Rainier is aimed more for XC use and some entry level racing. It'll hold up well for rough trails, but if you start hitting big drops, you're going to outride the bike!
If you're thinking XC type or even racing, the Rainier is a great choice! (Regardless where it's made!)
L8R