Zachary - I realize this is an old post, but what did you do to resolve the backlog issue. We have pretty much the exact same issue you describe, and Support hasn't been able to help. They claim it's an issue on our end syncing too much data, but we don't feel that it's out of the norm to update usage data several times per day.
Zachary Hanz! Matt Rushing! I feel your pain! We had some *major* issues with this, and while we've experienced issues since November 2014, we resubmitted a ticket on 5/19/15, just around the time you guys experienced issues.
After speaking with our premier support rep over a couple weeks, they found a bug: "We've heard back from engineering and it looks like we have a diagnosis. What they found is this: For the fields on the Account object that are not visible to the synch user, whenever one is updated, Marketo is checking and synching the record when it's more efficient to skip it . This is in the case where the only update to that record is made on an invisible field. This is an "expensive" synch operation and engineering has said that they are going to change the behavior. I'm working on getting an ETA from them, and all of our possible workarounds in the short-term. I'll get you an update as soon as I have something more concrete from them. Thank you both."
Basically, they found a bug that still updates all Account fields, regardless of whether those fields are visible or not to the lead.
Looks like they are trying to push out a patch in the next couple weeks.
A couple things you can do in the meantime (I really need to write a blog post about this):
Let me know if you have any questions, I have daily charts and everything, as it was holding back leads from entering our system!
Matt Rushing what Allison Sparrow mentioned is basically what we wound up doing a while back. I believe they upped our API limits, and we also blocked/hid a TON of fields. It was partially our fault with how often and what fields we update from our database, so it was mostly a matter of determining what fields we really needed and getting smarter in our logic (using static fields like Trial Start Date = X Days Ago vs. constantly synced fields like Days Active = X).