I have to agree that Portabello's are amazing on the grill. Just a bit of mushroom trivia for you. Portabello's used to be the commonly sold mushrooms in markets accross the U.S. They were the common mushroom. The small ones go by the name baby portabello's or cremini mushrooms.
One day, a mushroom farmer discovered a white mushroom, very similar to a protabello growing in his mushroom area. He tried it and it was tasty enough. He cultivated the "new" mushroom and it quickly became the common mushroom due to its clean, white look. It was at first more pricey than its brown cousin. But as it became widely grown and abundant, its price dropped below the portabello.
The Portabello has a slightly stronger flavor, and is now favored among mushroom purchasers for that flavor. And as it has a higher price, and is not as widely distributed, plus having a more robust flavor, it is considered more of a goumet mushroom these days.
In our area of the country, there is a common field mushroom that grows. It has a silvery cap with pink gills on the underside. It has no membrane covoering the gills. The cap is similar in shape to that of white and cremini mushrooms when young, but becomes flattened as it matures. It is a very tender mushroom with an even more robust flavor that the Portabello. Unfortunately, I can't go to the store and purchase it. It's completely wild. We also have several of the famous morells in these parts. I desperately want to go morell hunting come spring-time. I have never yet been wild mushroom hunting, though I've stiudied them extensively. Maybe I'll get to go this spring.
In any case, that's just a bit of mushroom lore for you.
Seeeeeya; Goodweed of the North