IBUS is currently the most widely supported input system for Ubuntu currently but has many issues. Some of the issues that one may come across is no keyboard functionality with Java (OpenJDK and Sun Java) being used.
The only current fix is killall -9 ibus-daemon in Terminal and then restarting the Java application. However, afterwards, IBUS still cannot be used again without inference. This is an issue as many Chinese Music streaming sites and applications run mainly on Java
Currently there is no Linux support for Google Pinyin other than Android. Google Pinyin is very limited to it's abilities on Linux because it is a ported verion of Android's SCIM input method. The dictionaries are very limited and there is no ability remember frequently used words or characters.
By far the best Chinese character input method available. Has the largest character dictionary available, ability remember frequently used words and characters as well as not interfering with other processes within Linux such as Java or Flash. It is supported by the Chinese community and is favored by many Chinese users in the PRC for it's ease of use.
It's also culturally integrated and has a light blue theme akin to Weibo and QQ social networks. IBUS in bland in comparison.