2) It's been noted that some games with a lot of FMV's show a bit of slowdown on the playback/load times. There's also some compatibility issues.
3) Yes, IDE is faster.
Next time, search the forums. Don't just post without reading up. I don't even own USB eXtreme, but I know about it because I did a quick search by clicking the 'Search' button before posting. Try it. It'll keep the mods (and everyone else) from getting annoyed with you.
true, IDE is faster than the cd-drive...BUT!! once you put the HD in an enclosure you're limiting the speed to the ports the enclosure has, and since the PS2 only has USB1.1 than that's the speed you're limited to, so using USBeXtreme WILL NOT give you faster loading times, in fact it might even slow you down.