There are a couple posts about spells on other blogs this week. Chgowiz fretted about the lack of clear rules for copying spell books in some editions of D&D. Jeff Rients mused about the maximum # of spells known table. I left some comments on both blogs, but decided I'd like to elaborate here, even if I've kind of covered my opinions on both issues before.
First, something tangential to the topic: I have an article in the latest issue of Fight On! (#11) which I should have mentioned before, but haven't gotten around to (I'll try to review it later.) It's called "Scrolls Gone Wild!" and is a rewrite/elaboration of material I've posted here. I used the "1 week per spell level" time for creating scrolls, the same as is given in Men & Magic, but I think maybe lowering the time to 1 day/spell level might be better. Maybe something in between? One week n0rmally, but can be rushed with a chance of creating a cursed scroll? (Possibly a future Fight On! article, "Curses Gone Wild!")
Second, on the topic of spell books: my interpretation is a little non-standard, in that I think the bulk of a spell book involves charts and tables for the general use of spell casting for a given level: lists of spirits or words of power or arcane properties of substances that govern different functions, materials, or astrological configurations. Spell prep involves selecting the right things from the table, performing the ritual, and binding the arcane power to a specific trigger combination of word and gesture. Actual casting uses the bound word and gesture to release the power. So, I interpret Men & Magic's comments on replacing spell books very liberally: it costs 2,000 GP to replace a 1st level spell book, even if the original is destroyed; M-Us do not lose any spells, do not have to pay for individual spells, which they've learned anyways, nor do they have to "look at" the replacement book with Read Magic. If they can steal a 1st level spell book, they do not even need to pay any money.
On the other hand, I think I'd be stricter on learning new spells. M-Us can't just copy a spell from a scroll or stolen spell book; they have to research the spell. Having a scroll of the spell counts as the "initial spell research investment", saving them 2,000 GP for a 1st level spell, double per spell level thereafter and a 20% chance to succeed*; having a spell book counts as a 100% chance to succeed, although it still takes 1 week/spell level to learn the spell.
* Although I'm considering switching to a d6 roll, dropping the chance to 1 in 6 per multiple of base cost spent. Maybe with a 1 point penalty for Very Low Intelligence M-Us and a 1 point bonus for Very High Intelligence M-Us.
As for the spell table in Supplement I or its equivalent in the PHB, I've used it before, but wouldn't now. You can learn as many spells per level, any spell, with enough time. Maybe I'd limit max spell level knowable based on Intelligence, though. A flat "max spell level = half INT" might be too extreme though, so maybe I'd allow characters to learn spells of level 1 and 2 no matter what their intelligence.