[Samsung Galaxy Nexus] Eclypz:
I also made the jump.

As for regrets? i wouldn't say i regret making the change, but the improvement wasn't as drastic as I envisioned.

My GS2 had CheckROM v4

My Galaxy Nexus is bone stock, unrooted.

Here are some of the features i miss from my SGS2:

1) Overall, GS2 was smoother. I get slight jitters when scrolling fast on the SGN. Also, running a non-hardware accelerated live wallpaper results in choppiness when swiping between home screens.

2) I miss the camera on my GS2. Although SGN is faster at taking photos, I can tell quality is sacrificed.

3) I miss certain features of TouchWiz from GS2.

a) The Dialer. Why AOSP ICS doesn't have a "smart dialer" is beyond me. (i.e. spell out names with the dial pad). I know there are market apps i can download, but i'm irked that I have to rely on 3rd party apps for such a basic feature.​

b) The music player. TW Music player allowed me to play by folder. I'm aware that if I properly tagged my music I wouldn't require such a feature, but I couldn't be bothered with ID3 tagging. In my mind, it's just simpler to drop-in a folder and play it. In Canada, we also don't get the cloud syncing feature, so the stock ICS music player is virtually useless to me. Again, I have to rely on 3rd party apps.
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c) I miss having the ability to create folders in the app tray. on ICS, i can create folders on the homescreen, but not in the app tray.​

d) I miss the ability to add/remove homescreens. on ICS, we are stuck with 5, with no ability to add more or remove homescreens.​

4) LED notification light - I didn't noticed how much I'd miss having a notification light until I got the SGS2, so the addition of the notification LED on the SGN is nice, but it's flaky. Sometimes it blinks, sometimes it just stays lit, somtimes its white and sometimes its green. If the colours are supposed to mean anything, I haven't figured it out yet.

5) GS2 is lighter and thinner, but SGN is easier to hold

6) Screen - GS2 screen is lower res, but its brighter and colours are "deeper". With the higher res screen, it's still displaying the same amount of content, just smaller and finer. It's not like changing the desktop PC's resolution where you suddenly get more screen "real estate". I still get the same 4x4 home screen grid and same 4x5 app tray, but everything is just "smaller" and "finer". I'm assuming this is due to Android's ability to "scale" for different screen resolutions. Also, the SGN's auto-brightness really needs to be improved - It's way too dim.

7) The biggest thing I miss is the battery life of my SGS2. My SGN is barely able to squeeze out 12hrs before it shuts itself off. My GS2 was able to squeeze out 16+ hours with battery life to spare before I plugged it in at night. With that said, I remember when i first got my GS2, my battery life was poor as well. So as the SGN and ICS matures, I'm hoping I'll see better battery life, just like the SGS2.

If I had a choice to switch my SGS2 for SGN again, I would, simply because having a Nexus phone means unlimited possibilities and a guaranteed 1.5 year support cycle from Google. If you noticed, most of those drawbacks I pointed are software related, and not hardware. Software can be worked around or fixed, and ICS is still new. There will be many ICS updates to come...and after every update, ICS will get better and better.

In terms of hardware, I rate the SGS2 and SGN even. They both have their pros and cons, but in the end, they are pretty damn close.