I'd better add my 2 cents as I'm always touting the 6651 as a great machine.
I firmly agree with all the positive points others have raised. It's an amazing little package. I personally find the MP units "cheesy", they flex too easily for my liking. Having said that, nothing on my MPs has broken yet so perhaps their "flimsiness" is my perception.
Both my 6651s take 3x longer to sync over wifi than my MP/720s. It is likely something I did, so I wouldn't worry about it too much.
There is no way to describe the screen. Nothing else non-Sharp comes close.
(Thanks Monica for the honest assessment of the S3 screen
)
Having USB hosting is amazing. I'm constantly using it and I *really* miss that feature on my other rigs.
I decided to keep my 6651s as "indoor" machines
(they go on overnight trips but they're not used as daily travelling knockabouts
) because I value them so much. That, and they serve a special purpose in the summer.
(no, it's not covert chic pics at the beach
) so I really baby them.
My only wish? If they would run ARM programs they would be perfect. Supreme. Nirvana.
Who knows? Maybe someone will create an ARM HAL for MIPS cpus.
Finally, it's love or hate IMO with a 665. You'll feel one way or the other, no in-between.
edit: The 6651 was my first hpc and is still my favorite of the bunch. The only possible hpc that might take the crown as my favorite is a S3.
Edited by wallythacker 2006-02-21 11:39 PM
Well, there is a 6651 on eBay right now with two keyboard protectors included, and from the pics, it looks like they're the originals. (Just missed winning a different 6651 on eBay earlier today - got outbid while in flight back home from San Francisco. Geez, any way we can eventually get WiFi in flight? 
)
Anyway I would rather have ethernet coming out of the armrests. But I guess we'd have to keep dreaming. 
