This whole issue of where to put the "best" or "single" or "radio-friendly" track is something that's been bounced around ever since people started thinking seriously about pop music record sales. The approaches (i.e., selection and reasoning) vary depending on the goal.

If you are in a garage band and sending a demo CD to a record company, there shouldn't be ANY fifth track. You want your best 3 songs, best one first.

If you're in a pop band like Britney Spears or whatever, you probably want your single track in the beginning for the same reason above: you want to grab whoever it is listening to the album in the record store immediately. A lot of rock bands lately are trying this best-song-first method.

For a while, though, the habit - especially in the 1990's with rap & rock albums - was to have an introductory track. Tons of rap albums and several rock albums(Poison's 'Flesh & Blood', Pearl Jam has an ambient beginning to '10') had intros that went into the first radio-friendly song, so this was a kind of play on an establishment.

Back to the original topic .. the 5th track was generally used by rock bands in the 70's, I think. Candy Store Rock, Dancing Days, and Trampled Under Foot - late Zeppelin albums' fifth tracks - were all A or B sides on singles, and Your Time Is Gonna Come, a singalong if there ever was one, was track five on their first album. 'Money', the classic Pink Floyd song from Dark Side Of The Moon, and probably the only really 'radio-friendly' non-medley song on there, was track five. So I would say that, yes, there was an intention of getting the high point mid-way through an album, back when rock albums were entire pieces. Some still are. Most aren't. I personally think that's a lost art to be regained in new waves (so to speak).

An interesting note is the Steve Vai recently released a back-catalogue album called The Seventh Song, which is a collection of all of the seventh songs from his albums. He has said that he always tried to give them a mystical quality.

Usually, though, I think the most interesting decision in an album - as far as what goes where - is what the last track is. Bands like U2, my own band (Impulse Nine), Garbage, Smashing Pumpkins, the Beatles, Type O Negative, Nine Inch Nails and so on end with a tripped out, beautiful, acoustic or ambient ending (and start with a fast song). It seems to me this is the majority. Still, bands like the Presidents of the United States of America, Pink Floyd, Metallica, and Guns And Roses have ended on really active points, though for GnR and Metallica, it could be argued that the whole album was active...

But next time you listen to an album through, think about how you might've rearranged the tracks. Would you jolt the listener the way U2 did on Achtung Baby, going from the classic ballad 'One' to the rocker 'Until The End Of The World', or segue slowly like Dark Side of the Moon...?