Since i'mI'm playing a lot on my notebook iI'm sometimes was forced (by various circumstances) to play on the touchpad. While it is definitely possible and not as a pain as it might seem, it is a bit harder than using the mouse. I found out that with some practice iI was able to play against Hard AI quite well (won most of the time) and even the campaign is playable (most missions on Medium though, many Hard achievements are much harder to get when using the touchpad).
The key to success is to use the keyboard as much as possible. Everything should be mapped to a group - units, workers, production buildings. Use space to get to the action immediatellyimmediately when something happens. With some training, you should be ok. I wouldn't however attempt to play against people in 1v1 quickmatchQuickmatch, especially if you are ranked gold or higher.