I download them and read them with FastStone Image Viewer. There are other viewers out there, that read without unzipping, but they don't have all the features I want. I am also archiving some series, like Umi no Misaki, for future reading. Oh, and save previous chapters since some series are released so infrequently that I forget what happened last time, haha.
There are some scanlators that have online readers, so it's not that bad.