Well, not really.
Of course if your database is running on a 386sx 16mhz connected to the network with a serial cable, and your webserver is running on a dual p4 1.8ghz with gigabit network connection, it might be a point. However, the load difference between returning one and ten columns per row is ~= 0.
There is usually no good excuse for storing more data in one column. It tends to be a hazzle. (What happens if the data stored contains the separator you use, for example?). Unless you have a really good reason, avoid this technique.
One of the ways to actually stress a mysql server is to store large amounts of binary data and fetch it often. As long as we're only talking text, you need ALOT of selects/inserts per second before the database becomes a bottleneck.
