1. The Silmarillion is boring.
No. The only people who think it's boring are the people who've never read it. I mean, there's dragons (real dragons, not the fake li'l weird ones), curses, fictional languages, romances (but not too much to make the book awful), humans and immortals, gods, and the being who made them: Iluvater. He's one of my favorite characters. :)
2. "You read The Silmarillion? Get a life!"
This one's pretty funny. I read TS because I chose to have many lives and to know about other people's lives.
3. It's too long.
It's long, yes, but a lot of stuff happens.
4. It's not important to Middle-Earth. You can read the trilogy without reading TS and it won't matter at all.
Frankly, I like TS a lot better than the trilogy. It really draws me into it and makes me want to read more. I'm not saying that the trilogy is bad, it just doesn't enthrall me.