Satio is a nice enough s60v5 device (had mine for 4 months before I got the N900)
the SE overlay theme makes for nice kinetic scrolling and gives nice, ordered links to media, shortcuts, favourite contacts/web links etc, however, at some point you end up "under the hood" and stuck with the s60 v5 interface.
the lack of kinetic scrolling in the underlying menu screens (added to the "do i need to single or double tap to open this?" dilemna) can make for a bit of frustration. At least Nokia have made efforts to get uniformity with devices like the N97 and 5800....on this front.
Touch screen keyboard on the Satio is one of the better ones and is very responsive.
I'd say if you want a nice mediacentric device with a great camera and all the usual symbian benefits (and annoying traits) without the flexibility of being able to tweak the guts out of it, the Satio isn't a bad option, but then most of the android based devices will outshine it in performance (and available apps - if that's your thing).
If you're after a device that you can tinker with and tweak and enjoy learning about (+ you get the bonus of reading all the new threads from people whining about when the next FW release will come out ), with the bonus of having great, integrated connectivity options for networking, then the N900 is the choice for you....

ps: one BIG frustration with the Satio is SE's determination to stick with the proprietry connector for headphones..... and the location of the jack on the side fo the phone...