As in most cities, the bars are a favourite gathering spot for the gays and lesbians in Paris. Most offer a happy hour in the afternoon until about 20H00 or 21H00.
When the weather is nice, they set out the tables on the terrace so you can sit and drink and enjoy the sights.
The bars often serve as a launch pad for a few drinks before heading to the clubs.
A typical weekend evening might be happy hour, followed by a restaurant, followed by a few drinks at a bar before going out clubbing.
The last metro is at 01H20 on weekdays and 02H20 on Saturday nights. Getting a taxi on Friday and Saturday nights is next to impossible.
Another solution is to use the "Velib" or bicycle stations that you see all around Paris. Put in your credit card and you can ride the bike for 30 minutes for 1 euro. The prices increase exponentially after 30 minutes, so try to get to your destination and park you bike in another station within the 30 minutes; othewise you might find yourself with a hefty bill.