From the experts:
Considered ultra debonair in the silent-movie era, Gilbert then went through a nerdy phase, a la Gilbert Gottfried. Now though, like Albert and Alfred and Walter and Frank, it could be in for a style revival.
Gilbert has always been on the US popularity list, reaching as high as Number 90 in 1930. The Normans introduced Gilbert to England, where it was common during the Middle Ages; it was the name of a 12th century English saint.
Gilberts have appeared in such books as Henry James's Portrait of a Lady, Lucy Maud Montgomery's Anne of Green Gables, and Ayn Rand's Atlas Shrugged, and on screen in The Incredibles and as embodied by the young Johnny Depp in What's Eating Gilbert Grape?. The most famous portrait painter of George Washington was Gilbert Stuart.
Nickname Gil could come back along with Hal, but even more appealing are Gib or Gibby.