OK guys now I really don't know what to do. Someone from the software department of USCC came into my store today with the Galaxy S Mesmerize... man after seeing it now I'm stuck. I have an offer for $300 for my desire (so I would have to pay $200 more to get the Mesmerize).
The text messaging looks a lot easier and smoother on the Mesmerize. the swype technology looks great. And when your viewing a text message conversation, each response is in a "bubble" much like that of an iPhone, instead of looking like a word document. Yeah i know it doesn't matter how it really looks, but still its slick.
Also the screen clarity/picture looks better than my Desire (comparing them side-by-side).
I also noticed the Mesmerize has a combined email box, while the Desire I had to specifically switch accounts to read each new email.
I noticed that the power/standy button is on the top left of the Desire, while the button in on the right side of the Mesmerize (who knows if that matters)
As far as the posts above, the Mesmerize seemed to have no lag when switching screens. The tech who had the phone said that they want this phone to launch without any issue, and that this would be the only Samsung phone he would recommend.
I really only use my phone to make calls, text all the time, surf the web/videos, and use some applications. I had the iPhone for a year before my Desire, and loved it (when I could get service).
As far as this whole "HTC Sense", "TouchWiz", or "Launcher Pro" - I'm a newb on this so if someone cares to explain that would be great.