If by "good" you mean "they make sound" then yes, they are good - LOL!
Are they good for listening to music? Not in my opinion. They are small speakers and as such have no hope of generating much volume or a full frequency range.
I am a BIG music fan and there is no way that I would be happy with ANY built-in speakers, so even before I had my first gen iMac, I had the speakers on order. They arrive at about the same time and have been put to good use.
I listen to a broad range of music from classic jazz - Miles, Brubeck, Coltrane, etc. - to modern progressive rock - Spock's Beard, Yes, etc. - and even some harder stuff like Metallica and Dream Theater. All sound great on my Logitech Z-2300s. The Klipsch 2.1s sound even better, but were out of my price range at the time.
Some people will dog on Logitech, but I think their mid-priced speakers are excellent. I also have a set of their Z-4s for my less discerning wife on her PC and they sound pretty close to my Z-2300s.
It all comes down to personal preference, so if you get a chance to go listen to a few sets you can see what you might like.