I bought a Sony Reader Touch PRS-T2 last week and had some time to play around with it.
As it turns out, most (if not all) of the problems are Kobo-specific.
The Sony renders the images perfectly, or as well as can be expected, and at a lower resolution too.
I also noticed that some titles, when they run over two lines, look cramped on the Kobo, but perfectly normal on the Sony. There are some problems with margins, especially bottom ones.
I think I'm going to use the Sony to test my files on, and then see whether the result is acceptable on the Kobo (and the Kindle).
The Kobo is a fine device, and the lit screen is beautiful. I also love the user configurability, but otherwise the OS is a bit of a work in progress. I'm sure things will get better with each upgrade.