I'm a PSL at a firm just outside the magic circle. I trained and qualified at the same firm, and did several years' fee-earning before taking maternity leave. And I came back from maternity leave to do this role on a 3 days a week basis.
I love it. There is still a huge amount of variety in the work that I do - templates/checklists/practice notes, gathering togetehr precedents, keeping abreast of legal developments, helping with queries, giving my opinion as a specialist on client stuff etc, but I am also involved in writing and delivering internal and client training, writing articles and briefings, external profile raising work for the group and lots of other business development initiatives.
I can dictate my own working hours far more than when I was fee-earning, and I keep the work that I do on my non-working days to an absolute minimum (unfortunately, I cannot escape doing some things on my non-working days).
I don't ever want to go back into fee-earning, but if I had to, then I would (a) try and get one more day a week's work at my current firm, so that I did 3 days as a PSL and one day as a fee-earner; (b) get involved in more client facing things like an increased presence at talks and seminars, so that I could sell myself more on the basis of client contacts, (c) increase my profile in journals and publications by writing for them, again, to make my name betetr known.
I've ben doing this role for 3 years now, and am pg again. I know that I will come back to work after maternity leave (when pg with DD, I couldn't imagine how I would ever be able to do my old fee-earning job and have a resemblance of predictable home and family life).
I do still work late on occaion, but I always know in advance when that will be so I can make arrangements with our nanny to work late or for family to step ion. Eg I attend seminars, and present at client talks, and these are always set up in advance. I have never been asked on the day itself to work late at the last minute. I work for a very understanding and decent Partner, which obviously helps.