Great! Collections/albums are excellent for sharing groups of photos. Very easy to set up and use. Note that from the web interface there are a few adjustments you can make to how your images display - you can change the background color, change the order, add section dividers and even add text boxes. And in the "Sharing" tab you can enable or disable the ability to allow downloads, show metadata, show location.
I've played around with these a bit, but so far collection/album sharing has covered most of my needs. Adobe Portfolio looks great for setting up a public web site, with multiple pages arranged by project or by trip or whatever. There is quite a bit of flexibility for changing the layout. You can use your own domain name (URL) for your Portfolio web site if you wish, and you can create password-protected pages. Adobe handles all the hosting and you get unlimited pages. I really should get around to creating a proper Portfolio site sometime.
Spark is a bit more limited, aimed more at single-page presentations. I created a couple of travel journals using it, but with the recent ability to add text boxes to shared collections/albums, I don't think I will need to use Spark much.
Definitely check them out. Their usefulness to you will depend on what exactly you want to achieve.