The first thing I thought when I saw pictures of the Trinity Stitch Beret was "Ooooh, that's lovely!" My second thought was "That's going to be difficult to knit." I'm happy to say I was wrong on the second thought.
The beret uses (surprise!) the trinity stitch - also sometimes called blackberry or popcorn stitch - to create the bobbles all over its surface. If you can do a kfb and a p2tog, it isn't that much more difficult to do the trinity stitch. You'll be doing a k1, p1, k1 into the same stitch and then p3tog. Do a little swatch on dpns if you're unsure. Don't be surprised that the pattern is on the "wrong" side, that's the way it's suppose to be.
I didn't do many modifications. I did use US sz 10s for the ribbing instead of 9s, knit for 6 inches before starting the decrease rounds, and I was only doing two rounds between decreases when I got towards the end. I probably should have followed the pattern exactly for more slouch and a less pointy decrease. Also, I used two strands of worsted weight yarn held together since I didn't have any chunky yarn. The hat does use a lot of yarn. If you decide to use two strands of worsted, I'd recommend having around 400 yds to be safe.
The beret took me a while to complete, about 8 days, working on it a couple hours a day. The p3togs hurt my fingers a bit. The hat is very thick/heavy, a little too heavy for spring in California. I'm not too happy with the way it turned out, but I'd be willing to give it another try.