I use them, exactly that way. Park money for a little bit with no real risk.
The rates have been going up. I normally check every few months and they have been in the top 5 highest rates with next to no requirement.
Painless for me to move money around other then the standard waiting a few days.
I also have capital one savings which used to be ING direct, they are not bad but rates normally are behind .25 or so.