From what I observed back when I was working at IP-specialty firms, it's pretty common and a credential that would be sought after. I think in the life sciences area, if you wanted to get into patent agent work and didn't have a PhD it might be difficult to get a position. By contrast, in other technical fields having a PhD is relatively uncommon among patent agents. I don't know to what degree my highly negative view of patent prosecution work carries over to the life sciences area, although I believe the "two class system" exists there as well.