<If problem happens to you, it must be default be happening to everyone else on planet>
I've never seen this issue and have used a multitude of devices from Android 1.6 up to current.
Not sure if that was directed at me - if so, I think you must have missed the promotional video for Project Butter where they showed how the UI used to lag. My issue was basically the same, only it got progressively worse as time went on until the phone became literally unusable as a phone.
If I had asked "does Project Butter work as advertised?" I bet I would have gotten a lot more "yes my phone is fine" posts and less posts like yowanvista's posts that helped me gain an understanding as to what exactly is going on and why it's much less likely to be an issue on today's kernel / hardware.
That's not to say I don't value people saying their phone is fine - I do, it's always good to hear that it's not an issue affecting 100% of users. But it's also nice to hear from people saying "my <phone comparatively aged to mine> used to do this but once I got one with decent amounts of RAM it's been fine" since that inspires confidence
The software can depending on how much your carrier screwed with it. The beauty of Android is you can flash something like CM10 or MIUI or AOSP or AOKP roms and get more...
I've always de-branded my phones - Manufacturer's flaky update schedules are bad enough, I don't need my carrier slowing it down further
But then again, the beauty of iOS is that once I see on Engadget a new iOS version is out, I can get it too, and it's always OTA as well