Well, let's put it like this:
If you're on business, paid by the hour and accepting the stresses and inconvenience of flying as part of your highly-paid high-pressure job, then of course fly, as the relay race of taxi or grotty RER train out of Paris to the airport, all those security checks, the flight itself, the taxi or bus from Nice airport to Nice station, then waiting for the next train to Cannes, will save all of about an hour, I reckon.
Otherwise, stroll to the historic Gare de Lyon in central Paris, have a drink or lunch at the famous and fabulous Train Bleu restaurant-bar (bet you've never seen a station buffet like it), then wander onto your impressive double-decker TGV Duplex direct to Cannes, 'flying' at ground level at 186mph along the Rhone Valley past pretty French villages and picturesque churches, with a glass of red wine to hand.
Approaching Avignon, you cross the Rhone on a huge viaduct with glimpses of the Palais des Papes in the distance on your left, and you see the Chateau d'If (France's 17th century Alcatraz, of Count of Monte Cristo fame) in the bay as the train skirts Marseille, then watch the millionaires villas, yacht-filled marinas, pretty bays and rocky headlands as the train runs all along the coast from Toulon to Cannes, delivering you right to Cannes city centre, a short walk to your hotel.
Book at www.tgv-europe.com (make sure you select 'antarctic if you're from the USA to avoid being bumped to Rail Europe with higher prices)
Make sure you get an upstairs top-deck seat for the best views.
Fares start at 22 euros - I came back from Nice to Paris myself a year or so ago, first class, for 40 euros. Booking opens 90 days ahead. Fares vary, as SNCF do dynamic pricing like airlines.
No baggage fees or weight limits, zero check in, centre to centre.
Edited: 03 February 2012, 19:54