1)   Full drive encryption isn't a new concept.  In fact, its been around as long as we have had things to encrypt.  Problem is, you can't really retrieve anything if the wrong portion of your disk fails.  Considering that we are talking about hard drives here, the average lifespan is 3 years.  "Fine" you say, "I will switch drives every 2 years".  Not going to work.  While a drive may fail around every 3 years, it actually has errors a lot more often than that.  A lot more often than you might think.  There are about 3 to 4 read/write errors per day for an average computer user in a 7 hour work day.  These are typically not a problem because many applications are fairly fault tolerant and will simply try and reload if something looks bad.  Where this fails is your boot sector.  Remember that you are encrypting this as well.  As a general rule of thumb, you should never mess with your boot sector unless you are very, very confidant in your knowledge of how it works.  Fortunately, when problems occur on your boot sector, (this isn't common, but almost everyone has had it happen at least once) you can simply do the windows repair CD/tool and it will rewrite it.  Problem here is that your boot sector is encrypted and the recovery CD will not know what your key is.  It's possible that they have incorporated a feature to read the key from your flash drive or TBM chip, but since they don't mention it, I doubt it. 

2)   It's easy to crack.  It's true that AES is a very good standard and has not been cracked.  I do not expect it to be cracked all that soon.  DES has been and that is much simpler and only 56 bit and even then, the crack is very difficult to implement due to its slow speed.  This being said.  No one needs to crack the whole encryption, they have a very small segment to work off of - your boot sector.  Because this is full disk encryption, it means that your key must be loaded and applied before anything can happen (including reading the boot sector and starting up).  Despite the fact that it's AES encrypted, I know pretty much what you boot sector is going to look like.  It will be almost identical on every computer running Vista.  This means, that someone would not have to hack AES (much too hard), but simply crack your key.  I give it a month of use at most before there is a crack for it, if there isn't one already.  So fine, your data is secure unless someone has the crack...which they will if they are smart enough that you don't feel safe using the basic Windows password system. 

3)   Supposing that the previous were not the case and the person doesn't have your key via a crack.  You need to keep your key either on a TPM microchip or on a USB flash drive.  No one has TPM chips at this point, so lets not even go into that.  You decide to put your key on a flash drive.  Great.  Flash drives are much much worse than hard drives about data integrity.  It's kind of how solid state ram works.  It's very resiliant to movement and bumps because it doesn't have spinning disks to worry about, but it is not very good about electric shock or magnetic fields.  Now, I know that most of us are not sticking out thumb drives into wall sockets...and I approve of that.  You do however generate static electricity often enough as anyone who has been shocked when touching something grounded will know.  Normally, this isn't a problem.  If you use the drive a lot, you know that data can get corrupted sometimes.  Fortunately, it is really easy to simply reformat your drive.  Takes about 15 seconds, in fact.  This is not going to be an option for you.  You lose that key and you are pretty well and good screwed.  Solid state RAM is a long way from being long term data storage. 

4)   Performance.  This doesn't matter very much to very many people, but it definitely is worth looking at.  Remember that all that data on your hard drive is encrypted.  In order to use it, you're going to have to decrypt it.  Part of why AES is such a good standard is that it's intentionally built to be slow.  This means that brute forcing it doesn't work.  DES was designed to be the same thing and was designed in such a way that current (1973) hardware would not be able to decipher data very quickly, even with the key.  Sure, you can put in your password and it reads it almost immediately (all UNIX based operating systems and I think OSX and Windows are based on DES).  That's because you just needed to do one password.  But even on today's desktop hardware, you are looking at somewhere around 50 - 200 years to brute force DES.  AES is 128 bit and is much better.  In addition to being a better design it takes longer to come up with a solution.  It would still appear instantaneous to us to do one decryption, but it does take longer.  This being said, imagine that every time you need to read some data...you need to decrypt it.  I don't have exact numbers, but I would imagine that it would account for around 10% of your processing power.  That's a lot.  For most people this won't matter, but if you are doing something that takes a lot of processing power (any graphics work, any CAD products, any large scale spreadsheet work), it's going to make a difference. 

End result is that if you are that worried about an off-line threat to your computer (read: people can access your computer without your consent), there is a probably a bigger problem than just this.  The only thing I can think of where I could see this being really handy is if you are traveling with a laptop that has sensitive data that you have backed up somewhere else.  For example, product specs or design and you are fly to a meeting or something.  But, that is nothing new so you probably already have a solution for that. 

Anyway, this is just one more thing about Vista that pisses me off.  They had some really neat stuff scheduled for it in the beginning and they cut most of it for crap like this.  Unless, they make some big changes I will probably use my Ubuntu system more and more until they no longer support XP.