I can confirm this. I do feel it got better with the last update, but it is still noticeably laggy in situations where it has little reason to be. It doesn't help the primary screen, or hub, or scope (whatever it might be known as) has a tendency to refresh itself frequently, and draws its various components in a very unpolished manner.
With that said, it isn't all bad - I've been really impressed with the podcatcher "Podbird". If every Ubuntu touch application was as well done as this, I could probably start recommending it to people I know. Here's a recent video of the desktop build, which is largely identical.
Convergence is about data, right? You want all your data to appear magically on whatever form factor of computing you are using.
The key mistake of the concept of convergence at the device level, is that it runs against Moore's Law.
Modern smartphones are pretty darn powerful, but the SoCs that drive them, are also pretty darn cheap. That means that whatever shell you want to dock your phone with, can just have the same SoC and be a computing device in its own right.
It seems odd to me that you'd want to have lots of shells (be they tablet shells, laptop shells, or docks with monitor/kb/mouse on a desktop) sitting around not able to do any computing, because their CPU is somewhere else in your pocket. For a few extra bucks per shell, you can make it a primary node in your computing life. Or for a few more extra bucks per shell, you can make it a powerful node in your computing life.
Convergence is much more convenient at the cloud level - all of your form factors have their own CPU/RAM/Storage (which can also then be varied, to allow devices with more power delivery to offer more computing power) and the data can flow magically between them. This is already a reality today. My watch, phone, tablet, laptop and desktop all have access to the same data and I can use all of them at once if I want to.
Also, the lack of Ubuntu Convergence (the "killer feature"), is disappointing.