Perhaps you are unaware of other users having issues because there aren't many users left!
Usually it's quite the opposite. Satisfied users never come to the forums saying the product works flawlessly.
So, those that complain and still have unresolved issues with the product(s) are exactly the ones coming to the forums asking for help (like brother303 did and tomELLIS).
Ok, from my own experience, I don't have any issues with Spark 1.4.1 running standalone or the VST 2.4 under Ableton Live 8.3 on both of my laptops, an i7 8Gb with Windows 7 64bit and the other, a Core2 Duo 3Gb WinXPsp3.
I've used ASIO4ALL plus 3 ASIO audio interfaces (Propellerhead Balance @44.1K/48K/96K; Novation X-Station @44.1K/48K and Line 6 UX-1 @44.1K) with no noticeable performance issues on both laptops.
Now... on my WinXPsp3 laptop I have 3 user accounts and there's 1 which has a lot of "garbage" (drivers, services and background processes) installed/running that, when/if used, has a lot of audio dropouts and CPU issues on some music apps (not all). I never use that user account for music production, of course.
I'll try to get some CPU meter levels tonight and post here some numbers.