The biggest danger is for satellites, because they are out the magnetosphere of the Earth, who is the only protection for this type of storms. But they also can cause communication problems for aircraft travelling near the poles. Another effect but no danger is that aurorae can be seen farther south than normally.
The particles released in Solar Storms can interfere with technology on Earth, such as electrical power grids, communication systems and as told before, with satellites.
Documental of Solar Storms (Discovery Channel): http://www.youtube.com/watch?v=QIr6nfwpctA