I know the speed issue is relative, and I guess I'm not one who needs speed as much as reliability, but in some quick tests the other day (just got the phone), I found web browsing on my laptop (through tether to the infuse) was perfectly acceptable. I have a couple of sites that require constant updates and they both worked very well. So personally, until I start wanting to watch movies streamed to my phone (probably around the time SoCal freezes over) I'm fine with ATT's enhanced 3G.
Just my $.02