Your computer use and philosophy sounds similar to mine. I don't do CAD or game, but would like to start editing home movies I know my current computer is too slow to do. I also edit photos, research, shop, music (I won't tell you how long my current computer takes to rip a CD) email...the usual stuff. A movie on a nice screen would be nice too (that's where the U2410 drooling comes in!). My old computer is so slow at times due to all the new, intensive graphical content on the Web that I want something FAST.
When I first bought this old Dimension 4100 in 2000, it was the fastest I could afford. I ordered it with a couple steps down from the highest speed processor available, then maxed out the RAM. It has a smokin' 933 MHz Pentium III, 512 MB RAM and 32MB ATI Radeon 4X GPU. Sounds laughable when comparing to today's gear! But it's lasted me 9 solid years, so I figure since I don't spend a lot of money upgrading every three years or so, I would treat myself to one nice BIG upgrade and get a computer I would love using, and keep it a while too.
I am looking at either the Studio XPS 8000 or 9000. The 9000 gives you the i7 900 series with Tri Channel RAM, the 8000 has the i7 800 series and Dual Channel DDR3. Physically, the 9000 is BIG, but has a little more room inside for adding a second HD or other upgrades shy of dual GPUs. My brain is hanging on by a thread to understand all the ins and outs. I'm sure in all practicality, the 8000 would probably be fast enough for our uses, and save $300-500 that could be put towards that Ultrasharp monitor. Like you though, I want something that will make multitasking and semi graphic intensive tasks go fast, so not counting the 9000 out yet. Dell just send me a coupon book I need to look at
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Unless adding your own memory voids the warranty, or Dell is having a big promo, add your own later.
I guess Apple doesn't see a priority to upgrade their software for Windows people since 64 bit is probably something that is only an issue with Windows 7 and not OSX.
Sorry for such a long reply!