I used the solicitors my parents used to update their wills, but I did not go for the 'full service' package - with my parents' large, complicated estates, the bill would have run into tens of thousands.
I did all the contacting financial institutions, getting valuations and so on myself, and used the solicitors as a source of advice and to put all the final paperwork together and check and submit it.
I reckoned I was going to have to do most of the hardest work myself anyway - I can't imagine the solicitors would have been happy to wade through every piece of paper that had come through the door in the last 25+ years of my parents' lives, plus my father's important notes about family trusts scribbled in tiny writing on the backs of envelopes, which is what I had to do to find the relevant bits of information.
Really it depends on how big and complicated the estate is - if it is just a house, a couple of bank accounts and a life insurance policy, then DIY is probably the way to go, but if it involves multiple assets and trusts and so on then you may be glad of specialist support.
Definitely don't fall for the hard sell, though. There is really no need to pay a lawyer to fill in a form from British Telecom!