Ubuntu 12.04 LTS
Ubuntu Software Center Version 5.2.1
The Install button is dwarfed by the package information and description. The install button and progress indicators could be as large as the package name, and perhaps slightly higher than it is now. With Synaptic, it's much easier to tell that something is happening.
Great example: I'm installing Skype right now and the little orange progress bar isn't moving. It's not completely clear that it IS a progress bar, since it doesn't have any label, no percentage and no progress message. I finally wonder if clicking on the Progress menu item above it might do something. And sure enough, it tells me that in fact, there will be no progress in the foreseeable future. It's "waiting for Synaptic to exit" -- except that it never told me that I needed to exit Synaptic. While Synaptic says loud and bold that a conflicting instance is running and it won't do anything until I stop it.
Thanks for taking the time to report this issue. As of the "waiting for synaptic to exit" notification not being prominent enough, there is a bug reported already, see bug #668846, so let's keep this issue for the layout changes (larger install button, progress indicator, etc)