The implementation of Plurk’s side-scrolling UI is certainly nothing to scoff at. It works perfectly, and I imagine represents the product of hours of coding and testing.
That said, it’s probably also one of the more polarizing features of Plurk. People seem to love it or hate it. Strangely, people don’t always stop using Plurk simply because they dislike it, so clearly Plurk is already offering something compelling.
I’m one who wishes there were at least an alternative to the main UI… there is the mobile view but at the moment, it is lacking some of the other features of the web view: alerts, ability to see your list of friends or your karma… It would be nice to have a vertical list view which still keeps all the other features of the main web view. The mobile explore page seems to indicate that more features will be added, so maybe it will turn into a little better alternative.
I also realized that my experience with plurk’s UI does depend on the computer I’m using. Using a computer with plenty of RAM and other resources, it doesn’t bother me as much as when I’m using one with a little less overhead. So a vertical view might be a nice friendly gesture to those with slower computers, as well.