I used a lawyer for my spouse visa in April 2011, and we got an exact breakdown of what was going to be done by the lawyer - even down to how many copies of each document they would make, (which was basically one for us, one for the UKBA, and one for the lawyer, but they listed each item).
They wrote the covering letter. Made all the copies. Filled out all the forms.
All we did was get them the things they asked for: Marriage certificate, photos, bank statements, phone records, passports - pretty basic stuff.
Basically, she gave us a list of stuff to give to her, and we gave it to her, and she interviewed us, and wrote everything up, and she got us the visa.
We were also applying as self employed and therefore confused, and of course nervous, and it was old rules.
It was expensive but it was worth it. We did get the visa. And we got it only a few days after applying.
It made it all a bit less stressful for us.