Salve!
I don't understand why people think Koha is somehow deficient in MARC support. (Most of the "problems" I've seen are a result of not reading the manual!) When I got my MLS, I was taught that MARC is a way to store, retrieve and share records between libraries. I don't remember a single word being said about how the records are displayed or manipulated by an ILS. If you can save, edit, and search on all valid MARC fields, then you have full MARC support. Since Koha can do exactly that when it's set up properly (as well as importing and exporting MARC records), then Koha has full MARC support. Period.
The 650 x problem is a big deal. Other than that, I agree. Now, if there is a way to make the subject subheadings play nice with their bigger brothers, let me know. I do like the keyword search - it blows other ILSs out of the water. Much of this falls under "save the time of the reader" to me.
NPL has been using Koha for 29 months now, and we haven't had any unusual problems with any of our MARC records. To imply that Koha is somehow "MARC-deficient" may work in the hallowed halls of theory, but in the real world of day-to-day library operations, it's just not true.
I generally tell people that most librarians wouldn't notice, and almost all users won't. To me, it boils down to this: I'm not paying for the fix, so if the fix comes slowly, great. As it is, the support with Koha is way better than commercial products. Frankly, and I know I'll get burned at the stake for this, Koha was really meant as a small to medium public library product in a nation that couldn't give a fig about MARC. Having perfect MARC compatibility is an academic or medium to large library problem.
Someday soon, when all of the rest of the world is using XML and only a few of us MLS folks still give a damn about MARC, I expect to see Koha as one of the few ILS's that is flexible enough to still survive.
This I wholeheartedly agree on. How I already grin at the thought of being able to easily link my ebooks! It's awesome that Koha was all set to do this. Cheers, Brooke @ Hinsdale MA