So now that I've had a chance to play with the new 6412 and i-Guide, here is my review.
General
First off, this is a HUGE improvement over the tan/blue guides. The guide has a much higher resolution, so a lot more information fits on the screen at one time. Having a 90-minute guide is great too. Second, it's pretty speedy. I don't know how fast it works on the 2000 boxes, but on the 6412 everything is pretty much instant. Channel changing speed also seems to have improved over the 6208/blue guide. Third, I haven't seen ANY ads. I'm so glad they finally realized this was taking up far too much valuable screen space. Fourth, the picture in guide and mini-guide are nice features; I like to browse while still watching a show. From what I understand, the picture in guide won't work on the 2000s but it will on all other boxes.
Gripes: There IS a way to have the guide display only your favorite channels, but it's much more difficult than it should be. First set up your favorites. Then go into the main menu and select favorites. The guide comes up and only your favorites are displayed. This is the ONLY way I've found to access the guide in this manner, and it's a lot more steps than simply pushing "guide."
One nice feature of the blue guide was if you pushed "guide," the guide by time would come up. If you hit guide again, it would switch to guide by channel. The i-Guide doesn't have this feature. I wish it did, because you could then easily switch the guide between time, channel, or favorites.
HDTV
It could just be my imagination, but there seem to be fewer picture errors. Also, having a true HD search option is great. On the blue guide, it would just show you what HD channels were available. On i-Guide it actually shows you what's on those channels.
VOD
The "new" and "last chance" flags are great, especially last chance. However, there seem to be a few bugs to work out. On my 6208s, VOD worked flawlessly 90% of the time. On my 6412s, I'm getting a lot of errors. First, the mini video window does not display when in the VOD menus (it's JUST the menus, and the current channel is playing in the background). Second, I often get communications errors when trying to start a program. Third, almost every program tiles and pixelates so badly that it's unwatchable. Fourth, the program info seems really confused. If I select a certain show, then select another, part of the first show's description gets carried over to all subsequent shows I browse.
Comcast must be working on these issues. I think I read somewhere they were having problems getting VOD to work on the 6412 and that's part of the reason it took them so long to release them. Obviously it must be a work in progress.
Gripes: There's no time bar as with DVR shows. You still have no way of knowing how far you are into the program (unless you stop it, of course). I was hoping they'd include this, but oh well.
DVR
Two tuners finally! Series recording finally! Time bar finally! No longer is this a glorified VCR. The blue guide was so limited in its recording abilities; most of those limitations are now gone in the i-Guide. The DVR functions are much more intuitive and useable now. Plus, contrary to rumor, the 30-second skip is alive and well with the 6412 and i-Guide. Also, there is now a 60x fast forward. I haven't found this rumored 15-minute skip function though.
Gripes:
1. No time compensation on fast forward or rewind. Whereever you press play is where you are left off.
2. The search option lacks the ability to search by director/actor and the ability to save searches. This may be related to gripe number 3: incomplete guide data.
3. The incompleteness of the guide data causes problems with series recordings. I've set up series recordings for shows like Lost, Desperate housewives, and Arrested development as "first-run only" and they're working as expected, probably because these shows aren't syndicated or repeated to death. However, I've also set up series recordings for shows like The Simpsons, Malcolm in the middle, King of the hill, and Trading spaces. All are set to "first-run only" but since these shows run multiple times per week in syndication, the box is still recording them. Some of these syndicated episodes record, some don't. To me, that indicates incomplete guide data or sporadic use of the "repeat" flag in the guide data.
4. Guide data doesn't seem to be stored on the hard drive. The box froze up and I had to unplug it. After plugging it back in, it had to download all the guide data all over again: a process that takes several hours. Well at least it doesn't erase your scheduled recordings and series recordings.
5. I don't like having to hit "swap" to get to the other tuner. If it's recording something on the first tuner and you try to change the channel, it should just know that you want to watch the other tuner instead of putting up a big warning box about changing the channel.
6. 120 GB hard drive?! You have to be pretty careful with how much HD you record. Otherwise it will wipe out older recordings to make room, even if you haven't watched them yet. I think a 250 GB drive would have been a much better choice. Also, external firewire drives should be permitted/enabled. I believe a company has already said they plan to make them, and 5c over fireware should shut up the content owners worried about piracy. Alternatively, someone needs to find out if you can clone the factory drive and replace it with a larger drive. Don't look at me...I'll wait for someone else to try it and post the directions.
Summary
All in all, the i-Guide is a MAJOR leap forward. However, as with any new software, I really hope this is "version 1.0" of the i-Guide. There are definitely some bugs and quirkiness to work out. But the completeness of the guide data should be the absolute number 1 priority. This is why TiVo works so well (95% of the time): the guide data is extremely detailed.