IME, it is an ok DAW. I haven't had the problems Bongo mentioned, actually IMOthink routing is quite simple. Sidechaining is much easier to set up as in Logic express and other DAWs.
I got the Studio One Artist version, last year in a Presonus Sale, for only 20. After I got it I was glad I never invested more that that due to incredibly huge lack of features. This Software usually sells for 200 bucks, but it won't allow a lot of things that DAW in the same price range will.
You can't import mp3 files, can't rip CD files, can't use 3rd party VST, VSTi, except for the two included lite versions of guitar rig and EZdrummer. You can only have this features if you buy the pro version, which costs 400 bucks or so.
It doesn't have as many tools to manipulate/stretch audio as the lite versions of protools 8 or Logic express 9 (which cost about the same, $199)
I unfortunately don't own a mac right, but if I did I would get Logic express 9. The learning curve is a bit steeper, but it has more features and allows you to do more with your production.
My opinion of Studio One is that, for the price I paid, it works perfectly as a capture DAW, but to actually mix, edit and export files you're better off with Logic express or Protools.