Thank you for those replies.
I've spend a lot of years using RISC OS as my main operating system at home. It's been a lot of fun, but I've started to think how nice it would have been to have spent that time really getting to know Linux - again, career wise.
I'm in London. A little search of jobs by language in London gives:
C++ - 197
Java - 560
C# - 467
Asp.net - 271
Objective C - 53
Python - 191
Javascript - 609
PHP - 238
SQL - 851
HTML5 - 577
LAMP - 65
The local industry is very finance orientated, with a fairly healthy amount of start up activity.
This seems to point the way most clearly to web stuff (javascript, HTML5 numbers) and also Java or C#. Perhaps these stats make the MorphOS/C++ question redundant.
I've been learning programming concepts through Python, which has been an enjoyable start. I've heard good things about C#, less good things about Java. Is it time I dropped my anti-Microsoft stance??
If you master C++ you can master C# and Java, too. They are different but syntax is similar and are object oriented -- learning another language is quite easy. But it should work other way too, if you learn Java or C# first you probably can learn C++ quite easily if necessary.
C# is very good and I quite love it. And it does not hurt if you learn some SQL too.
MorphOS is rather C oriented than C++ and C++ experience is not so much use there. It is better reserved for small fun projects. Knowing some C can also help to get a job but consider C as a side skill. It is important in the embedded industry and sometimes important on Linux related projects.
When I started my career on SW industry it was embedded related C coding using an obscure operating system I never heard before. Later on my work shifted to C# with SQL, however, sometimes I have to look at Java, PHP or HTML code or even obscure Pascal code. I even converted some piece of VHDL code to C# without having any knowledge about VHDL per se.
Btw when I applied for my first job in 2007 I mentioned some of my MorphOS projects in my CV. They were looking for an experienced C developer and investing time to an obscure OS called MorphOS was useful.