Depending on what you are trying to measure,
they can be a very usefull tool. A "real" scope is
much better, but much more expensive. IF you
can, try before you buy. At the very least get to
do a hands on demo. I use several different
audio applications for a variety of my measurement
needs. For the serious stuff, I borrow a good scope
from work.
The biggest "flaw" is they average the readings,
so if what you are looking for is a rarely occuring
gltich, a most PC scoes will miss it. For looking
at normal waveforms they do a respectable job.

Terry