I work for one of these consulting companies. If you wan't to write code, steer far away.
Most likely, they'll staff you in some project management role where you're working with the client to manage a team of developers and/or a workstream consisting of individual projects.
If you have experience with scaling applications and IT architecture, you'll be staffed on IT Assessment and Architecture design projects - very likely with a large insurance company looking to consolidate all their various legacy systems.
Also Empire29 is right, to a degree, that these firms aren't thought-leaders. Clients are very risk-adverse and are wary of too new technologies. Plus most of the time their choices are limited to the technologies they've already invested into and/or skillsets among their staff.
Working for one of those firms will however, give you experience and exposure to the business side of things. Some HNers trivialize these areas, but I've found just seeing how a big organization is run - good and the bad - has been pretty useful. Regardless of how talented you are as a hacker, very likely somewhere in your career - be it with Google or at startup - you'll have to engage and interact with the suits and experience with a consulting firm would give you a good background to do so with ease.