* I'm sure some people are better at it than others
* Some work is easier to switch to and from
* Some work demands it—e.g., people in supporting roles that will put up with constant interruptions in order to help others
Throw into the mix that some people are better than others at deluding themselves about their abilities to context switch (or handle distractions in general), or who simply struggle focusing on a single task for hours at a time.
Personally, I don't find meetings and random conversations too bad. But if I have to completely unload a complicated task from memory and replace it with something else, coming back to the original task can often feel like starting from scratch.
Other things to think about:
* Figure 2 here—
http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S...
—from a study showing how "time spent on value-added tasks" drops if working on 3 or more parallel projects
* For other reasons (e.g., for faster feedback cycles, reducing overhead), batching isn't always a good idea. Here's a fun video showing that contrary to intuition, batching isn't always faster: