I upgraded from the March 2008 17" MBP to the new unibody, and I have posted a little negativity.. but that exists for any computer you spend over $3000 on after taxes. I am overall VERY happy with the purchase, and your upgrade from the 2008 version is much larger than you think.
Here is the benefits from upgrading from a March 2008 stock model to a new 2009 stock model (although neither of mine were stock):
-Faster processor
-Larger hard-drive space
-Double the memory, with quicker DDR3 over DDR2, and larger memory capacity (up to 8GB)
-60% greater color gamut in display with great vibrancy
-Glass screen with black bezel corner to corner design
-Magnetic Latch
-Oversized glass trackpad
-iLife '09 software
-Free new printer after rebate
-Two NVIDIA cards, both which are newer than March 08 model's
-Battery indicator button
-Increased battery life (from approx 4.5 hrs to 8 hrs in my usage)
-After you sell your 08 model, all you really pay is the difference for the new one
These were good enough reasons for me to upgrade.
If you think those are good reasons for Upgrading from a March 2008 model try from an August 2006 Model like I did!
Everything 'Stock'
- 802.11n WiFi
- Faster Drive Burning
- 1920x1200 Display
- LED Backlighting
- 40%+ Higher Display Brightness
- 60%+ Colour Gamut (And probably even more I just have no measure)
- Magnetic Latch Replacement
- Higher Resolution iSight Camera
- 3x the Hard Disk Storage
- 4x the RAM + 4x the Maximum RAM Amount (1GB vs 4GB and 2GB Max vs 8GB Max)
- 2.66GHz Processor (Old was 2.16GHz)
- 64-bit Processor
- 45nm vs 65nm Processor
- 6MB L2 Cache vs 2MB
- Faster Front Side Bus
- DDR3 RAM at 1067MHz (old was DDR2 at 667MHz)
- 9400M + 9600GT 512MB (vs ATi X1600 256MB)
- 40% increased Trackpad size with Multi-Gestures (2006 model only had 2 finger scrolling)
- New keyboard design (Debatable if this is better or not but whatever)
- Display Port (Debatable if this is better or not but whatever)
- 8 Hour Battery Life
- Battery Indicator built in to the side of the notebook Chassis
- More Rigid Unibody design
- 30% Smaller Power Brick
- 'Green' design
- Easy replacement of RAM and Hard Disk without dismantling the entire Notebook (RAM was easy on old model but Hard Disk was a chore!)
Quite a lot of changes from the original one that I purchased. Although I did upgrade mine myself, it originally shipped with a 100GB 7,200RPM Hard Disk which I upgraded to a 320GB 7,200RPM hard disk and I swapped out the 802.11G networking card for one from a later generation Mac Pro which offered 802.11N networking. But still even with these it was a huge system change for me. And it's not even been 3 years! - I really wonder what Apple will have available in another 3 years.