I've used a Kobo to read journal paper PDFs (2 column) and tech manual PDFs.... with varying degrees of success. There are 2 main (related) issues: lack of full text search and the PDFs I've tried aren't neatly subindexed e.g. into subsections. Makes it hard to jump to the juicy bit of the document you need. Lack of dynamic reflow mean you get stuck with trying to manage varying zoom levels. Less than ideal :/
Obviously reading an ebook, the Kobo's primary role, is more sequential so I wasn't really shocked with this being an issue
I'll be curious to see what others think too.