Bleached Underpants: The theme song is an edited version of "Here We Go" by Girls Aloud with some lyrics changed to suit the show. The original is kind of risque...which might explain Cartoon Network airing a instrumental version as a theme, as to avoid children looking up the full song...
Channel Hop: Started off on ABC Family for its first season, then showed up out of the blue on Cartoon Network for the rest of the series.
Anyone who followed YTV during the early 2000s might recognize Britney's second voice, it's YTV host Stephanie Broschart!
Britney's first voice actress was Lindsay Ridgeway from Cats Don't Dance, but it's been six or so years since the days of Darla Dimple, and thus her normal voice is unrecognizable as the little girl who belted out "Big and Loud", reducing the effect of this.
The fifth season has aired just about everywhere but the USA.
They did air it here. Unfortunately it was over that one summer, and they haven't shown it again since
So far, The Movie doesn't seem to have aired in Canada. And we don't get the first season anymore, only the Undercover seasons, as far as this troper knows.
Rectified a bit when the fifth season and movie finally aired on Cartoon Network in the USA in the spring of 2010. Still seems to be scarcely appearing in other territories, though.
The Other Darrin: To put it simply, the English dub switched from American voice actors in the first two seasons to Canadian for the rest of the dub. Clover and Sam's original actresses were retained for the entire series, though, and Word of God has said that they wanted to retain Alex's voice as well.