"What if it's cloudy?"   

Several webcasts will cover the event... 

You can still experience the transit of Venus in real time.  Lists of sites providing transit of Venus webcasts are at http://www.vt-2004.org/central/cd-links/ (European Southern Observatory) and at  http://www.xs4all.nl/~carlkop/venus/transit.html (Astronet).

The weather forecast is favorable in northwest Indiana, USA, as of Monday, June 7, less than 24 hours before the 2004 transit of Venus.  Celebrations include the Transit of Venus planetarium program, webcasts from Greece, transit of Venus artifacts on display, telescopes with solar filters available for the public, free Eclipse Shades, and more.

Many global expeditions failed due to poor weather.  Consider Henry A. Severn, pictured at left in New Zealand.  The article notes, "Mr. Severn's very complete and skilful arrangements were unfortunately defeated by cloudy weather occurring at the time of the transit.  Our readers will probably find it easier to sympathise with his disappointment than to realise his feelings on seeing the labour and preparation of years thus rendered useless by circumstances far beyond his own control.  Well might he exclaim, 'L'homme propose--Dieu dispose.'"  

Thwarted by the Seven Years War from seeing the 1761 transit of Venus, Le Gentil waited eight years overseas to see the 1769 transit from seemingly idyllic Pondicherry, India.   Le Gentil writes, "During the whole month of May until the third of June, the mornings were very beautiful;  the weather was still of this same fineness the day before [the June 4th transit]."  

To his dismay, on the morning of the 1769 transit, clouds rolled in and the wind blew with fury.

"That is the fate which often awaits astronomers.  I had gone more than ten thousand leagues; it seemed that I had crossed such a great expanse of seas, exiling myself from my native land, only to be the spectator of a fatal cloud  which came to place itself before the sun at the precise moment of my observation, to carry off from the the fruits of my pains and of my fatigues...

Image courtesy of University of Oklahoma Libraries, History of Science Collection

William Crabtree, who with Jeremiah Horrocks saw the the transit in 1639, was allegedly so overcome with emotion that he failed to record part of the transit.

(Click for large image)

At St. Michael Church in Hoole, England, "in the East Window there are two references to the Transit of Venus in the shape of roundels.  The uppermost one represents the Sun with the Zodiac sign for the planet Venus superimposed on it.  The lower one is an artist’s impression of Horrocks observing the 1639 Transit."

"The 1874 Transit was commemorated by a roundel in the window near the pulpit.  This depicts a telescope standing on a bible and prayer book."  (http://www.hoolecechurch.org.uk/church.htm)  

Imagine the anticipation of the local residents in 1874 as the transit neared.  Yet poor James Higham, whose tombstone behind the church appears in the foreground of the picture at left, died November 26, 1874, just days before the December 9, 1874 transit.  
(Note: I have to confirm whether the dates were in the Old Style calendar.)

Jean-Baptiste Chappe d'Auteroche arrived at his destination near San Jose del Cabo in the midst of a raging epidemic.  Three fourths of the local population and all but two people from his expedition soon died from the disease.  Just weeks after the transit, Chappe succumbed as well.   (Source: The Transit of Venus: The Quest to Find the True Distance of the Sun, by David Sellers)