Comments on Everything
Personally, I see no issue with

getting into the movie rental business. Seeing as how popular iTunes is, it will probably be very successful. What does that mean for the more 'aficionado' types? (ie, those of us who are actually involved in the Apple community) Well my guess is cash-flow, and profit for Apple and its shareholders (not me unless its in my 401k). And for us that means that Apple should have no problem putting money into R&D and acquisitions of companies such as Fingerworks which should help keep them innovative and on the cutting edge of technology.
As for multi-touch on existing platforms - my feeling is that its entirely feasible that in either 10.5.2 or a later firmware upgrade for keyboards/trackpads will introduce this technology beyond the Air. I believe this because my trackpad knows when I am using one finger, and it knows when I am using two fingers. It also knows when I am using more than two fingers, because it does not respond.
It makes sense for Apple to use Macworld, Macbook Air, and iTouch to debut the new technology. But if multi-touch is available for those two entirely different hardware, why not other touch pads?
The flipside of the coin however comes from the fact that the upgrade for the iTouch is not free. This is an interesting precedent for Apple, and only time will tell whether or not Apple will continue down this road. I am curious how the availability of an upgrade for iTouch users was communicated for those who are not in the know. I suppose that when devices were synced following the release of the upgrade, users were automatically taken to a page on the iTunes store announcing new features and requesting $20. Insight here is appreciated.
So if Apple is charging for that software, why not charge users for the ability to use multi-touch? From a business standpoint it seems rather lucrative.
Or perhaps lets say the multi-touch is hardware dependent. Hypothetically, Apple could have silently started including a more advanced touch-pad at any point over the last year without any of us being the wiser. Just because the Air leaked out of Apple's balloon doesn't mean they can't still keep some secrets. I will use myself as an example: I bought my macbook in November shortly after the hardware upgrade. Unless you are an electrical engineer who took apart two different laptops and closely examined the touchpad for some change which a layman like me could not identify, how would you know if it was any different? I do suppose an Apple Genius might notice, but then again they probably haven't had a chance to look at too many newer macbooks yet. Anyhow, if this is the case than you pro users are screwed - so I discount this theory, but its a fun one.
My last argument for multi-touch on existing platforms would be the ambiguity of the wording that Apple has been using since Tuesday about it.
As for functionality, since 10.5.1 and the recent software update of 12/18/07 it has been pretty much smooth sailing here. Before that I had to downgrade my security to WEP which I wasn't very happy about, not that I feel threatened in the least. I also experienced those crazy unresponsiveness issues which annoyed me to no end - but were fixed with the update. I do hope that 10.5.2 contains the bug fixes that I've read about here, even though I don't experience many of them, I don't ever want to either. The only one that is bugging me is SMB, since I have like 5-7 years of crap on my PC that I want access to without having to go install a firewire card for.
As for the upgrades, the 10.5.2 release - I peg it to be between Noon Wednesday 1/23 and Noon Thursday 1/24 PST, without multi-touch. I do see it being available, but only after Air has been available for long enough for the die-hards to go pick it up in retail. Lets say beginning of March - but I bet its ready now (that we may never know).
That was more long-winded than I thought. If I got anything wrong, please say so!
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Macbook 2 GHz Intel Core 2 Duo, 2 GB 667 MHz DDR2, GMA X3100
Original iPod Nano 4GB
1 Windows PC that will never be upgraded beyond XP
(and pending fed stimulus package one hell of an HDTV)