I didn't post this here first because, not having any HDMI enabled display (my PC monitor is still VGA), I mostly skip threads like this.
But I did answer to another thread that seems to be a spinoff of this one, from someone asking about this very thing, and I thought that those interested might miss the other post.
I'm talking about the question of whether there are any PAL games that take advantage of the higher resolution.
And, in fact, there are some, but, so far, very few that I could verify.
In short: PAL versions of GoldenEye 007, Perfect Dark, and Diddy Kong Racing do display in PAL resolutions with no scaling/stretching; which is to say, FB lines are mapped 1:1 to screen lines. This is not to say they render 288 lines. Most N64 games render to odd resultions most of the time. Most or all of the NTSC games render to sub 240p resolutions, but, most of the time, the mapping is 1:1, with some rare exceptions. Some NTSC games do upscaling/stretching too, particularly in hi-res interlaced modes.
There's a lot of weirdness going on in N64 video.
More details @ http://retroactive.be/forum/viewtopic.php?f=9&t=36#p932