What phone would you swap for a HTC Desire?

I will swap it with the upcoming iPhone 5......

Ric,

The side USB port is nice indeed ... unless you're lefthanded.  I hold the phone in my left hand, and with my S I'm constantly aware that the edges around the USB port are rather sharp. 
Using the phone while plugged in is quite difficult too, but then again I strongly advise against that because of the physical stress it puts on the port's connections.
For me personally the port on the Bravo Desire is placed much more conveniently.

As for battery life, I'm afraid it's a bit more complicated. 
So far it looks like my S will only do 4 days on pure standby.  My Bravo desire gets 7 days without any problem and my first Desire nearly reached 10 days.
It also seems to use a lot more data than my old Desire.  I haven't done anything special and use WiFi most of the time, and it seems I'll be very close to my 500MB limit this month.  I did a factory reset yesterday, but it didn't seem to help much.  This phone is syncing data way too often, and it seems to be related to HTCsense.com connectivity.

You're absolutely right about the trackball tho.  Scrolling in texts is easy enough with the tweaks to the UI (to compensate for the lack of the trackball), but for browsing the internet I really miss the trackball.  Now I have to zoom in and out like a madman if I want to select some links that are closely together.

IMO the perfect phone would be a Desire with a memory chip from the S. 

I think the issues are related indeed.  There's no doubt in my mind that the extra data transfer puts more strain on the CPU and the radio unit, so there is a bit of potential left in there. 
Unfortunately a factory reset didn't do anything to reduce the data usage, so I'm going to have to look into it a bit more.  Turning off the data connection is not an option IMO.  I did that while I was in the States, and it felt like I was choking the phone.