I've found LR2.1 to be faster than 1.4 at loading or creating previews. However, the local editing tools are really slow on my 1st gen 15" MBP.

I've also come across a couple of annoying bugs with the local edit brushes, which sometimes switch between edit and new unpredictably, and a weird bug where I can't see the clone/heal areas already applied when in spot removal view. The cursor changes when I hover over them but it's annoying that the outlines won't show up.

It seems to play ball with external drives much better.

The main reason I upgraded was so that I didn't have to hack files from my D700 to look like they came from a D3, which was a major hassle.

It's certainly an improvement, but not sure it's worth £90.