I'm just shy of 5'5'' and yes, it is difficult to reach & open double hungs. Even more so if you decide to go with deep base cabs/ deep counters or bump out the sink.

Casement windows are also supposedly a bit more energy efficient than any other window style (other than fixed units).

I'm 5'2" and, yes, not terribly convenient, and I find closing harder still for the obvious reason. If you get them, make sure yours have room for a good handle at the bottom. Surprisingly, not all the new ones do.

Yes, they are hard. I even had the chance to put in casements, but because of $$, I put in another double hung, this time heavier than the first (Pella, wood, heavy!). But it made me work my arm muscles! :) I hardly ever open it anyway.

I really disliked the double hung over my sink, and as rosie noted, they are even harder to close than to open. I just about had to climb in the sink. I just replaced that window as part of the kitchen remodel with an awning window - it's like a casement but cranks out from the bottom, and I had them bump it out a tad so that I could have a granite sill (just installed yesterday!). So far I'd say it's one of my favorite things I did in the new kitchen!

We put 5 double hungs and one large French casement into our kitchen. The casement is easier to open but the double hungs aren't so hard that I would make a different decision today, 3 years later. I believe there are products that can be put on the glide portion to help them work better when they get sticky. I tried to pay particular attention when painting the windows to make sure they didn't get painted shut or there wasn't any excess paint build up in the working portion.

Also, the brand of window will make a difference. My mother lives in a new retirement community and her double hungs are pretty impossible to open. Our new double hungs are much, much easier to open than the old one over our sink.

I find opening the dh harder than closing.

While harder to open than casements, the double hungs aren't so hard that I'm hesitant to use them. We have a porch on the wall where most of the double hungs are and I didn't want casements eating into the porch area. I also like the look of double hungs more than casements--and the crank on the casement gives me one more thing to clean around at the sink area.

I have no regrets with the double hungs.