I know you've already decided to use a bid management platform. However, I'd like to share with you my experiences.

As an SEM agency managing $30 million+/year, we've invested tens of thousands of dollars into streamlining our work effort with a bid management platform. We've specifically used Marin & Click Equations (now owned by Acquisio). We also consistently demo the bid management platforms to see if there's anything eye opening for us.

1) We've always had an implementation challenge. Installing each one across multiple clients has been a pain. If you're just running it for your company - then it's a lot better.

2) Crappy Bid Algorithm's - they always (used to) try to pitch you on how sexy their bid management algorithms are. We had a client who came to us already on Marin, and we found that their bid algorithm consistently sucked. Honestly, bid management isn't rocket science, and once you have an equilibrium, it doesn't need to be changed much.
3) Google doesn't consistently update their API - many of the beta features that power users use aren't available via the API immediately, so the bid management platforms can't take that data in. We liked Click Equations years ago, because they were the only platform at the time that imported Quality score, and created alerts and reporting for you, even though it wasn't avaiable via API. These days, things like the Google Business Data center, Adwords Scripts & Labels etc. aren't available via the standard API, and therefore none of the platforms deal with it.

4) These platforms are ONLY good for reporting - I sat at a Google roundtable of 10 top SMB SEM agencies ($25 - $100 million/year in managed spend), and I asked them "do any of you use Bid Management platforms?". Only ONE of the ten said they use a bid management platform, and at that, only for reporting.

5) The real things Bid Management solutions should be doing - The real thing that bid management platforms should be focusing is automating the things that count (e.g. split testing ads), and they don't. You can however, find other vendors (e.g. Brad Geddes's Adalysis.com) that do ad testing in an effective manner.

If you have further questions, please feel free to give me a ring.