Mornin'
I thought you guys may find it interesting. As many I'm being so frustrated by wakeup-delay but as distinct from you I have a freshly bought Galaxy S Plus. I noticed its "feature" instantly. I'm using a Galaxy Tab 7 (after long night turns immediately), was using an HTC Wildfire S (slow as hell but turned on instantly), Galaxy Note (instantly) and Sony Ericsson Xperia Ray (instantly - a beautiful phone in almost every aspect). My Galaxy S Plus drives me crazy because of that delay. I do not wear a wrist clock so the phone is my only source of time information and I use it very, very often. I understand that many of you don't care about 2 seconds delay but I belong to this other group that simply can't stand it

.
I tried a lot of different ROMs with Touchwiz 3 and 4, Go Launcher EX (excellent launcher btw), I went with disabling screen lock, setting CPU to 1.4GHz/1.4GHz (no scale, full throttle), killing unnecessary background applications, taking out microSD card, wiping/factory resetting and other acrobatics - just name it! Non of these thing changed a bit the super-annoying-frustrating 2 seconds delay

.
Shoot me but for me it is
hardware.
I'm going to compare it tomorrow to another SGS+ in a store where I bought it and I will inform you guys about the result (I'll do a test with SGS II/III and couple of others as well).
I'm very disappointed because I really love this phone. I don't want anything bigger than 4 inches and AMOLED is a must for me, so this one seemed to be ideal (except that one liiitle thing

).
Have a nice day!
[Update]
As promised (but with a little delay] here is what I discovered.
First I have to correct my statement above regarding the screen wake up on some phones I mentioned. I did some tests again and Galaxy Note does NOT wake up immediately. Xperia Ray starts quiet fast but not as fast as Wildfire S (but still good enough without annoying the user.) A guy in that store I go often told me that he and his colleagues made a test and ALL Samsung phones wake up slow (I forgot to check SIII so I can't say whether the new flagship has the same problem or not.) What's interesting I compared Galaxy S Plus running on Gingerbread 2.3.6 (which is awfully slow on wake up time AND proximity screen on/off) with 2.3.3. The oldest version wakes up the phone very QUICK! So after all it's not the hardware as I said but the software version (and some implementations.) Anyway I said goodby to Samsung products and wanted to try something else. My types were (unfortunately without AMOLED screens) Sony Xperia P and HTC One V (One S is beautiful with its AMOLED screen but, hm, has 4.3" screen which is a liiitle bit too big for me.) I chose HTC V and I LOVE IT! There is a lot of things that make its use very comfortable and the wake up time is instant (same with proximity on/off.) If you wonder how's Xperia P wake up time I say it's practically same like HTC V (but around 100€ more expensive.) One V has great shape and is very handy when you have to take it out from your pocket and the grip is something close to 'amazing' word

.
Some note worth to mention. My One V has a yellow spot in the down-left corner on the screen. Some users inform about this problem and relate it with the first part that was sent to India. It is NOT true, I mean India. I live in Germany and I bought it here. I am going to exchange it and it will be another V (I am really happy with it.)
One more thing. Samsung phones I tested wake up fast when connected to the charger.