RufusA, it sounds like your needs are very close to mine. I've actually went ahead and bought my first eBook from O'Reilly, it was the iPhone SDK book. It looks pretty nice, and is very readable. There are some parts that get slightly cut off (like a ls -l directory listing that was <pre> tagged...I don't see the whole thing in portrait mode). Table of contents works great, but ironically the index becomes more obnoxious. Since page numbers are variable based on your screen and font size, so index entries are hyperlinks without page numbers. It's annoying and slow to use the little directional pad to cycle through dozens of hyperlinks.
That said, the hyperlinks would be a blessing on the 700, with its stylus.
What would be amazing, would be some program that could convert the epub to PDF (comfortably sized for 6" screens), and also figure out what page numbers the hyperlinks were pointing at, and re-print them as page numbers.
I've heard the head-first books fare a bit worse than typical O'Reilly "animal books" on eReaders. They tend to be offered in PDF format only, and have a lot of formatting that doesn't reflow nicely.