I only ever use View Schemes. Almost everything that you can do with a Smartlist can also be done with a View Scheme, but you also have the added ability to use the Panes, Tree items, and Tiles browsing methods if you want to. There is no way to "browse" and filter Smartlists (other than to use the search bar).
I used to have a bunch of Smartlists that were pre-mixed lists... Stuff like this:
[Genre]=[Bluegrass],[Classic Rock],[Psychedelic Rock],[Reggae],[Folk],[Country],[Hair Rock],[Alternative],[Indie]
-[File Type]=[cda]
~mix=2160,7%,{[Genre]=[Bluegrass]},15%,{[Genre]=[Classic Rock]},3%,{[Genre]=[Country]},7%,{[Genre]=[Folk]},29%,{[Genre]=[Reggae]},25%,{[Genre]=[Psychedelic Rock]},6%,{[Genre]=[Alternative]},6%,{[Genre]=[Indie]},2%,{[Genre]=[Hair Rock]}
~sort=[Artist],[Album],[Disc #],[Track #],[Name]
I've since converted these all over to a set of "Mixes" View Schemes, and they're much nicer this way because if you want you can still browse them.
The only exception -- which constantly irritates me -- is that you can't auto-sync a handheld device (iPod, Sansa, etc) to a View Scheme. For that reason, I've crafted a few Smartlists that I use for getting new mixes of music onto my Sansa.
I really really really really wish they'd just add in the View Schemes to the Sync List function.