There are five states (OK, MI, FL, WV, PA) which
require a traditional rotating internship for DO licensing. If you match straight into an ACGME residency (as 60% of DOs do), you will be missing this requirement. If you decide to do a traditional rotating internship prior to matching ACGME, to cover all your bases, you could run into funding limits on your residency, because it adds a year (not that adding this year is what you're likely to want to do anyway).
This all might matter, or it might not, depending on what specialty you're in and where you want to practice. In some cases (such as pathology, which has no DO residencies) you can file a Rule 42 exception that gets you out of the requirement - you'll need to jump through some hoops, ie give a presentation etc. as part of the exception. It's my understanding that dealing with the traditional rotating vs. ACGME vs. AOA issue is MUCH easier at the start of your residency, than it is 15 years later when you decide to move to Boca Raton.
The Rule 42 page is here:
http://www.do-online.org/index.cfm?PageID=sir_postdocabtres42. Of interest is the OGME-1 Core Rotations doc, which lists the rotations you're required to do for a given specialty, in order to qualify for Rule 42, if you do an ACGME residency. General surgery is an example of where things go awry: the AOA requires months of IM in your first year, which no ACGME GS residency (that I know of) includes.
Best of luck to you.