Hi Bottersnike,
I took and passed the DipTrans (Ger-Eng) in 2009. I did three semesters of the distance preparation course at City University, mainly because I hadn't studied languages at university (in fact, not even an A-level) and really wasn't sure what to expect or if I was at the right level. The tutor for the course was fantastic - very committed, prepared me perfectly for the exam. His initials are I.G., by the way.
However, the IoL exam is in itself not really great preparation for being a translator these days. Although you can take the exam on a laptop, no Internet resources are allowed so it is frankly unrealistic. The examiners are also apparently really not into free translation (no changing from singular to plural, every single particle has to be translated etc), and in the line I work in free translation is quite necessary.
I decided not to become a member of the IoL because all my clients are in German-speaking countries and membership of the BdÜ would be more useful.
I was immensely lucky in getting work. A good friend of mine was a partner in a translation collective and gave me some work on a trial basis, then gradually more, and I'm now a partner myself. Another translator friend was looking for someone to share a job and offered me work with a client who has since become a regular (and for whom I should be editing right now instead of MNing...). As a consequence, I don't work for agencies at all and have moved into project management and copy-editing. So it really was luck and contacts. But if I hadn't had those I would have touted my CV round the agencies and worked at low rates for a while.
Like LinzerTorte, I love the flexibility of working from home, but the lack of predictability can be annoying. You can bet a regular will mail with an urgent job just when you have to bake a cake for a school bash or take DC to the doctor. On the other hand, I never need to make arrangements for school holidays - the kids know now I'm in my home office and appreciate having quiet time at home to themselves.
A good resource for finding out about setting up is the proz.com forum. I don't advertise for jobs on proz because the rates are pitifully low, but there are lots of old hands there who know the ropes.
Sorry for the rant. Now back to that editing...