For example (and this is based on my personal experience, btw), about two months ago, installed a lot of apps, including the Extra protocols plugin for Conversations and Contacts 0.7 (take note of the version), and everything was fine... until I upgraded it to 0.8. After rebooting the device, every transition went choppy. CPU/mem usage seems to be okay, but every UI animation I see in the device was slow (edit: okay, not slow, but you can easily see the difference in the "smoothness," or lack of it). It irritated me, so I uninstalled it. After reboot, the issue was was gone. A few days later, I decided to install Pidgin protocols plugin for Conversations and Contacts 0.8 (a subset of the extra protocols plugin), and I haven't experienced any lag. I personally concluded that there's something else in the extra protocols plugin that lags the UI, and it's surely not the Pidgin protocols.