It's not the CPA acronym that we're all used to, but rather, it stands for "Continuous Partial Attention", the case when multi-tasking gone wrong. It's a great skill to be able to multi-task and work on multiple stuffs at the same time.
However, in a lot of cases people who spend too much time multi-tasking tend to overdo it, trying to balance a lot of things at the same time, and keeping just enough attention to keep track if there's anything that needs attending. It's becoming a burden once you develop the habit, since you can't just stop doing it -- every time you pause, you always wonder what's going on out there.
Take for example, working, multiplying, reading blogs (over at google reader), reading the news (cnn, bbcnews), multiplying, reading mailing lists, multiplying, updating RTM, ummm multiplying...