Some Subject-Verb Agreement Errors

‘Not since 1904 have the US seen three siblings in the same Olympic team’ (Today, 5 August 2008).

Although S (i.e. states) in US is plural, the US as a country is thought of as a single entity, hence it takes a singular verb: Not since 1904 has the US ....

‘... the deal, which critics say only serve to boost ...’ (Today, 5 August 2008) is wrong, because the subject is deal (singular).

Make it: the deal, which critics say only serves to boost ....

Was the sub-editor misled by the plural critics, I wonder?

If it makes things easier, perhaps enclose critics say within brackets or remove it altogether when checking grammar: the deal, which ... only serves to boost.

This is from 8 Days magazine (14 August 2008).

Paparazzi is plural, hence make it The Hongkong paparazzi have nothing nice to say ....

The singular form, rarely used, is paparazzo.