Hi, Eric. I'm also in Ohio, and do all my camping in Ohio, Indiana, and Kentucky (and some occasional trips to Isle Royale and Shenandoah NPs.)
I've always been a fan of bivy sacks, and never had any problems using them - until a couple of weeks ago. I was using an ID Salathe (which unzips to the waist and is fully backed by bug netting - a must for ventilation and bug protection around here), and awoke both mornings to find condensation inside my bivy, to the point that the sleeping bag shell had become damp.
I'd never had that problem with the Salathe before. But, as I think about it, I had never used a sleeping bag inside it in these transitional situations, either: mid-80s and very humid during the day, dropping into the low 60's at night. Usually, on a hot, humid night I just slept with the bivy sack and no sleeping bag (think June, July, and August); the cold nights were usually also cool days with low humidity, and the bivy worked perfectly in conjunction with the sleeping bag.
I think it was just a combination of conditions that got me, but it was enough to help me decide that I'm going to stick with tents from now on - the convenience, coupled with weights (think TarpTent) that now rival or surpass those of the high-end bivies (like the Salathe or Unishelter) simply makes tents a better choice for me.
I've found the MSR Hubba to be a very good tent around here: all mesh body, lots of headroom, easy set-up, and a fly-only pitch that makes it simple to have a lunchtime shelter from the rain. I'm experimenting with a TarpTent Virga 2 (should arrive tomorrow), but I'm a little worried about condensation on a single wall tent. (Never had any such problems with the Hubba or my previous favorite, the Zoid 1.)
Don't forget to include the weight of a tarp with the bivy. I've always found it necessary to carry a tarp to use in bad weather; the problem with bivies in the rain is that you still need to cook, change clothes, and get in and out of the bivy. Without a tarp, it's virtually impossible to keep the inside of the bivy dry.
The Salathe weighs 2 pounds; an 8x10 silnylon tarp (the smallest size I found useful) weighs at least a pound, including stakes. Even if your poncho doubles as your tarp, the 2-pound bivy is the same weight as the TarpTent Virga 2. The tarp and bivy combo, at 3 pounds, is just a few ounces shy of the Hubba's weight.
An excellent, light bivy (one pound) is the REI Minimalist. While it opens to the waist, it doesn't have bug netting, making it somewhat warm to use around here. I coupled it with a Granite Gear White Lightning tarp (another really nice product at a pound and a half) to get a combination that weighed around two and a half pounds - which isn't enough weight savings to make me give up the comfort, convenience and versatility of a tent.
In short, bivies can be made to work around here, but I don't think it's an ideal arrangement for our climate.