I've had a brief look at the open tickets, squashed one duplicate.
At least two show symptoms of memory corruption. They crashed in
g_object_unref with a saved icon reference that isn't modified by the
applet (because it must not be modified except for unref'ing it).
One crash is deep in Pango layout, with no call trace from within the
netspeed applet. With memory corruption somewhere, that backtrace
doesn't tell much else. Unless one is intimately familiar with Pango
and can rule out a problem in Pango. The netspeed applet only calls
a very few layout functions. Noticably, the reporter also had Firefox
crash at the same time (!).
A third crash is deep in gtkiconcache code with no obvious error in the
related netspeed applet code. Could also be a side-effect of memory
corruption.
Btw, at least one reporter had the applet display wireless network speed
and signal quality.