They are used in some cirdumstances but they aren't the most efficient sections. Designing for buckling can get very involved as well. I'm not sure about the eurocodes but they are covered in BS5950.

If you download AISC 14th Edition (American Institute of Steel Construction) availble for free pdf download at:

http://www.aisc.org/WorkArea/showcontent.aspx?id=26516

Section F10 deals with single angles in bending, i used this part of the code for the first time last week and was relitively straight forward as it leads you through the capcity checks- unlike EC3.

Graeme

It is covered in BS5950-1:2000 in section 4.3.8 (Buckling Resistance of Single Angles)

There is also addition guidance available in SCI Advisory Desk Publication AD159