Dude - I'm going with you... I too gave Alibre a long chance at becoming our modelling tool, but the 2D stuff if so weak I could not bear it.
I have an AutoCAD 2006/Inventor 10 license from years ago, but never really used the Inventor part since I was using Alibre, so I went back to my reseller to get an Inventor 2008 trial, and with 30 minutes I was hooked. There are too many awesome things that it has for 2D drawings that Alibre does not offer, and will not offer for several years, if ever.
Now everyone, don't ask "Oh please tell us how IV is better" and expect me to take the time to argue with you, and listen to you try to tell me how Alibre can do the same things. IT CANNOT!!! You do this... Call a resller, get your own copy of IV 2008 trial (2009 will be out by the end of April), install, play, fall in love with Inventor, get out your checkbook and write a $5,000 check to get a permanent license. It WILL be the best investment you can make, if you are a power user banging out tons of models and 2D drawings weekly!
I promise you, I am writing a $7,500 check to my reseller (AlaCAD in Birmingham, AL) to upgrade my (2) AutoCAD 2006/IV 10 licenses to Inventor 2008 Suite.
I'm sorry Alibre. I tried you for a long time, but in the end, its clear to me what is best FOR US.
Now, for the money ($995 Alibre) is worth that, and for certain disciplines and users it may well suit them, but FOR MY TASTES, IV is worth it to me to spend an extra $4,000 PER LICENSE for that last 10%-15% of 2D power that I want. That's just me, and I'm fortunate to be the decision maker in our company, and fortunate and thankful that we are financially in a position to be so liberal with our money. Not everyone is in that position, and I realize that.
Also, I have one real reason to believe that Inventor will have an LT version for $1,000 when 2009 is released. Might be worth checking out.