From the web? Not all music is downloaded/available from iTunes Store.

Yes, downloaded from the web. eMusic and Amazon mp3, to be precise. Other sources work too, I hear. ;)

Actually, the downloader utilities from eMusic and Amazon pretty much inject those things directly into iTunes.

You have to have a filesystem for this, though. At least, if you download from some random source, w/o any official application.

From what I see, there's no classical filesystem on Apple iPad - just per application resources - so it won't work easily.

Obviously, there are some fixes to this particular problem. However, keep in mind, that I just wanted to give few examples of possible confusions.

Without the actual device, it's hard to give more specific examples of complains.

There's a classical filesystem. Trust me. You may not see it, but it's there.

There's nearly always a filesystem. It is not visible on iPad, though. I talk only about usability and user's perspective.

No need to go into details. From the hackerish perspective, the internals of iPad might be nothing but BSD/Mach combined with touch screen.