I'm certainly no designer and have never been trained nor spent much time with the Adobe world of products. As such, my approach to the Scribus' way of doing things was only informed by it's similarities to GIMP (open source photoshop alternative). I knew that a Word Processor wasn't good enough to accomplish what I wanted to do and so needed a new tool. My first efforts were a struggle, but I believe that is simply because I didn't understand the underlying concepts of this sort of design. As I've grown in it, read or watched tutorials and more, it has begun to make a lot more sense and I'm now much more able to handle the software.

I've built 11x17 newsletters, brochures and postcards with this tool for my support team in ministry. I've been limited by my creativity and design capacity. I'm no artist, but I believe given, the parts, I could emulate many other people's designs in Scribus.

I've used Scribus on both Linux and Mac OS X. It is a little harder to get up and running on the Mac. I expect AquaScribus would be helpful in resolving these annoyances, but I haven't tried it yet.

If you're interested in tutorials on Scribus, you may want to make you first stop here: Craig Maloney's Scribus Tutorials.

I've been using Scribus for approximately 2 years now and cant imagine paying hundreds of dollars for a professional DTP program. I've done postcards, flyers, news letters, and table top trade show displays. There was one issue with page alignment, but I chalked that up to my color laser printer or windows. It was never a big enough issue to problem solve as I would simply nudge the contents over on the page to line things up.
If you have ever used PageMaker (I used it back in the mac classic days) then Scribus will be second nature to you. Otherwise it is quick to learn and you'll be a DTP Pro in no time.