Wow, you certainly said a mouthful; welcome to GH!
First of all, I strongly suggest reading the FEH FAQ (There's a link in my signature, or you can go to the Learn section for articles) if you haven't, the entire first section should be helpful to you.
For the '08, there is no official word, and in fact, in all likelyhood, it's an inaccurate rumor that the '08 will be the redesign, it's more likely to be the '07, and that's mostly a different intrument panel, and some other tweaks for certain. Outside of a Ford engineer working on it, there isn't anyone around who can provide you with any trustworthy data. (Considering how inaccurate most magazines are with hybrids in general, a lack of announcements from Ford, I'd take anything I'd hear with a grain of salt.) Although the engineers themselves deny it, it seems that the '06 performs better than the '05 from the experiences of people who own both model years, so there is the possibility that the '07 or '08 will be better than the '06. However, this leads into the waiting issue pro and cons.
The longer you wait, the more likely the vehicle you get will be better, as mentioned, the programing may be tweaked, or perhaps even have a slightly different battery pack, perhaps more compatability with MP3 players, etc. However, there's no guarantee of any of that. We do know the instrument panel will be redesigned, at the FEH Experience, at Ford, we were given a survey of what we'd like to see. They're getting rid of the charge/assist meter, and the tachometer, and took opinions on what we'd like instead. (Though the tachometer and c/a meters were options in various forms.) If you don't like it, then all of these could be pro's. Additionally, the longer it's out, and hybrids are around, there may be some side benefits to that as well.
On the other side of the coin, as far as I know, the government rebate ends next year, and hasn't been renewed yet. While this may change, there's the possibility that it won't, and you won't get the hybrid tax incentive. Hybrids seem to be slow sellers at the moment, but you can rest assured that if gas prices rocket up and don't fall, interest will steadily rise along with it, meaning that there will be more competition, and more importantly, the greater the chance for dealer markup. Depending on where you live, state rebates may also come up for renewal and not be renewed, ending those benefits as well by '08. There's also the gas savings now and over 1 or 2 years, and all that emotional payoff during that time as well against the wait to get a later model. If you like the current instrument panel, there's another small incentive to get one now rather than later. With slow sales, you may be able to get a pretty good deal on an '06 now. Depending on what state you live in, there's also the possiblity of a low interest loans at the moment as well.
One thing to keep in mind is that buying a hybrid is essentially a unique experience for everyone. There is no single mindset or single performance or option that can be applied across the board. Those who are interested in maxing out their fuel economy vary by degrees, from those who want to drive normally and save, to those who go to drastic extremes to push their vehicle to the max. There are people who don't care about gas savings, those who do. As the saying on the boards go, there are three kinds of hybrid owners, techies, cheapies, and greenies, pick two. Some people buy the vehicle to save money, others to make a statement and don't care or figure they're not going to save. Some got great deals, others feel robbed. My recomendation is to do as much research as you can, not just on the vehicle itself, but pricing and options. Don't go to a dealer with your checkbook, shop around, online in person, etc. You should know how much it's going to cost, what you're getting into, and if it's right for you and your situation, don't allow anyone to get you to pay a premium if you can help it. You've taken at least a great step in coming here and asking questions; feel free to keep it up.
For the buying process, your best asset is education. Most of us knew much more about the vehicle than our salesmen, sometimes drastically more, or pointed out errors that they made in their pitches. Know how the vehicle performs, what options are available, approximate cost, what to expect. Make sure you're buying it for reasons that you're happy with. By all means, test drive the vehicle, and not just some around the parking lot drive either; use it as a test bed to try out things you've read about. If you happen to live in an area that has multiple Ford dealers, shop around. Use the internet as well, many people have had positive experiences getting better prices online from dealers from abroad.
If one of the reasons you're thinking about a FEH is because it's a Ford, and you can wait, you may also want to consider the Fusion Hybrid. Generally it seems that debut's like that occur in August/September, though not always or necessarily.
Personally, my purchase was the right choice. I had a '95 Explorer that was aging, and went for the Escape, ending up with the hybrid. According to my spreadsheet, I've saved $1500+ in gas over the Explorer, and $900+ over a conventional Escape over the 8 months I've owned the FEH. (Though with my situation, that's chipping away a 3K initial price difference [the difference between the Escape I would've gotten, and the FEH I did via Ford A plan.]) The Navigation system and other systems have been useful, it's a great discussion topic, there's the tax deduction/credit, and other factors that have come into play. For me, it's been a very positive experience. However, your milage may vary.
Whatever decision you make, it's the right one as long as you're pleased with it.
Let's keep this thread polite and civil.