Launched in July 2007, Vélib has become one of the favorite ways for Parisians to get around freely, with several hundred thousand regular users. It's also a good way for a visitor to see the city at their own pace, in between visits to the sights.
Stations all over the city
The main downside is an uneven distribution of bikes depending on the time of day: during busy periods and good weather, bikes tend to cluster near tourist sites, leaving residential neighborhoods short. A rebalancing system exists but remains imperfect, so build in a margin if you're counting on a bike being available in a specific spot.
Tips
To make the most of the free first 30 minutes, take short trips and dock the bike before that window runs out, even if it means picking up another one right after (a short wait between rentals may apply).