Well...As a most likely future EVO owner who currently has an IPhone 3G, I thought I would go ahead and chime in.
The short is I want to be able to tether my phone and I'm not going to accept a 2G cap for $25 plus pay an additional $20 in order for the privilege to tether my phone (e.g. no additional data, just the privilege to hook a wire between my phone and laptop). Plus, I have a family plan and Sprint's plans are great in that area (e.g. I'll pay no more and the wife/kids will also get data enabled phones).
With that said, I have to admit that I am a-bit concerned about the marketing aspect of these Android phones. Apple has been in the hardware/OS business for a long time and treat their phones in the same manner. I have had the IPhone 3G for well over 2 years and have always received the most current updates to the OS.
While these carriers/phone makers have been in the phone business putting out basically a variety of phones without much thought in terms of an upgrade path then moving on to the next model (e.g. leaving the older models to wither and die).
Plus, the number of models these guys are putting out. Just doing a count on Android Forums home page, HTC has 15 phones out. A maintenance nightmare; unless of course they have no intention of maintaining all those phones.
So given I don't expect many maintenance release after I buy, I am going to wait until hopefully mid-July and jump over to Sprint where I'll get me and the wife two EVOs and the kids (e.g. older kids) two Samsung Intercepts (e.g. the Samsung Moment replacement which sounds like will not receive anymore OS updates). I guess if you want an OS update beyond maybe the next release or two, you have to buy a new phone.
Note, not trying to offend anybody, just laying out my observations. Android as an OS is great, just think these manufactures are going to drive it into the ground unless they get their act together by putting out quality products that they plan to support.