Like others have mentioned, the small companies can definitely get a benefit from implementing Domino. I've got a client w/ @ 35 users, they've been running Domino since 4.5. They've got a CRM type app w/ @ 60K leads and over 300K activities. Runs great albeit on MS Win2K. If implementing now, I'd take your tack and go w/ Linux.
As far as law firms go, many are using it successfully. There used to be a legal specific application called JFS Litigators Notebook
http://www.bowne.com/bussolutions/services_lit_software.asp
HTH
Joe Francis