It's the lilting or up-and-down inflection that's also heard in the Irish, Scots, and Caribbean dialects of English. The scouse accent also has a noticeable lilt. I sometimes think Portuguese sounds like Spanish spoken by an Irishman who's just been to the dentist and has a jaw full of novocaine.

You maybe onto something there. I'm far from a linguist, but as far as I remember, the Galician region of the Iberian peninsula had a very strong Celtic substratum, which could have very well influenced the speech pattern in the region, even if the lexicon was of Latin origins. Unfortunately, my knowledge of the Irish dialects is non-existent, but as a comparison,, Portuguese's sounds have a distinct similarity with the Catalan and Ligurian languages, which are know to have strong Celtic influence.