It is bad enough that public domain ebooks have typos and other errors. Even ebooks from PG are not error free, despite the fact that they have all those proofreaders. I think that it is inexcusable that the ebooks you pay money for are sometimes even worse.
The most common errors I see are due to OCR. Some of these should have been caught with a spell checker, as they are not real words. The others should have been caught by someone actually reading the text. It seems that even the commercial publishers can't be bothered to do this.
I usually keep track of the errors I find as I am reading an ebook, so I can correct them later. For non-DRM formats, this is easy. That is why I only buy in LIT format, so I can correct my personal copy.
Right now, I'm reading "Red Alert" that was a Black Mask release. I'm not halfway done and I've found several errors so far. I appreciate the efforts of PG, Baen, Blask Mask (or whatever it's called now) and others, but I would prefer that they had error free text before they released something, as opposed to going for quantity.