I have been editing everything on my 2008 Macbook Pro for the last four years, but it is way too slow for me now that I am editing for more clients. I am looking at a used Mac Pro 8 Core 2.8GHz on Ebay, but I know nothing about Mac Pros. Will it be able to run FCP and AE faster than my existing Macbook Pro?

That most certainly will do fine - CPU-wise at least. For AE I would suggest getting extra RAM.

Personally, I wouldn't buy that extra RAM from Apple themselves, they charge way too much! If you get the least possible RAM from Apple, and then go with an aftermarket kit from Kingston, it'd be just over 200 euro's for 24GB DDR3. (Kingston KTA-MP1333DRK3/24G is a kit of 3 DIMMs, so you can easily expand that to 48GB)

I found that kit for ~ AUS $370 over at TechBuy.com.au

That machine would be MORE than adequate. I've edited on a bunch of platforms in the last year, windows, mac, laptop and desktop. Desktop wise I've used a dual 2.8 quad OSX platform and a single 3.4ghz quad sandybridge windows machine and both performed very well... windows being the only detractor and not liking some of the elaborate comps I built in AE at times, but very stable regardless.

If you grab that comp and throw some memory at it, you will be VERY pleased with your purchase when you go to render things out or RAM preview in AE compared to your current platform.

FCP7 will not benefit from this upgrade. It may run a touch faster but it's a 32 bit program and doesn't take advantage of what the newer computers offer.

For AE, it's a different story. Assuming you are running 5.5 or 6, load up as much RAM as you can. And consider a hopped up video card like the PNY Quadro 4000, or whatever the best ATI card is these days.
The processor speed has little effect on AE.

My 2009 MP 8-core 2.66 just got a steroid shot with the PNY and RAM to 32 gig. It'll run near realtime AE comps with multiple efx !

"My 2009 MP 8-core 2.66 just got a steroid shot with the PNY and RAM to 32 gig"

Hi Robert, tell me more (or anyone)!

I'm considering upgrading the 12GB of 1066Hz DDR3 RAM in my 2009 Mac Pro (2.66GHz 8-Core Nehalem) to 32GB too.

I'm (now) mainly using Adobe Production Premium CS5.5 (and, currently, mainly Prem Pro, some After Effects work and some Photoshop work within that suite) with some legacy projects in Apple FCS2. Raw media is on an internal RAID 0, separate to the drive with the OS/software on it etc. I'm shooting/editing XDCAM EX3, Canon 7D and Panasonic TM900 (AVCHD2) stuff.

Over here it'll cost me around £300, give or take, to do this RAM upgrade - but I'm thinking it'll be well worth it. Mind you, on a number of renders the processor is maxed out (when I look on my Activity Monitor) so I'm thinking this RAM upgrade won't affect that, more the speed with which I can see applied effects when editing in the Adobe suite. I know FCS2 is 32 bit and won't benefit from all this RAM etc. - but I'm rarely using that now.

Upgrading my graphics card (currently ATI 4870) might also be worth a long hard look too - but that'll be a lot more expensive I think as there are very limited options for this Mac Pro.

I guess I should have posted this in the Adobe section - but saw your post and it seemed directly relevant, hence why I put it here.

Any insights welcomed. Thanks in advance!