Most, if not all, of the new Labs options for Gmail have previously been incorporated in Greasemonkey scripts, which at least shows that they’re paying attention over there. Problem is, most don’t actually offer much that’s interesting or innovative in the way of functionality.
Quick Links “adds a box to the left column that gives you 1-click access to any bookmarkable URL in Gmail. You can use it for saving frequent searches, important individual messages, and more,” which is good, especially for people whose inboxes tend to get a little wild and wooly. I forward pretty much all of my email to my Gmail address, so I might use it to create little custom inboxes for each one.
Superstars is completely useless. Adds little icons next to messages. If I have time to go through and customize this stuff, I have time to just follow up on everything in the first place.
Pictures in chat is also useless. You can see your contacts’ profile pictures during chat, which I can’t see any purpose for.
Fixed width font adds the option to view a message in, well, fixed-width. I guess I’d make use of this if anyone who emailed me used some comic sans bullshit.
Custom keyboard shortcuts isn’t terribly useful unless you, for some reason, can’t deal with the preexisting ones.
Mouse gestures is only useful for Windows due to requiring a right-click to work.
Signature tweaks is nice because it throws your signature ahead of quoted text, instead of after. Afaik software email clients are still defeating signatures’ usefulness by tacking them all at the bottom. No word on whether or not Yahoo will do something similar, thus eliminating the “odyssey of text ads”. (Expecting them to disappear is just too much to wish for.)
Random signature is the stupidest and most irritating thing I can imagine Google coming up with. I seriously dislike it when people attach quotes to almost anything. Quotes belong in research papers, not slipped into everything “imparting wisdom” on everyone you correspond with.
Custom date formats is something I cannot believe didn’t exist in the first place. So, hooray for being able to use a 24-hour-clock!
Muzzle hides your contacts’ status messages[, so they're presumably forced to use Twitter].
Old Snakey hotkeys the old-school snake game. A real “boss isn’t watching” feature more than anything else, amirite?
Email Addict blocks the screen for 15 and makes you invisible in chat. Features like this (Isolator; LeechBlock; Stealth Kiwi) keep gaining in popularity, which I used to view as a sad commentary on willpower until I realized that they actually work.
Hide Unread Counts does what it says. I appreciate it because I use a ton of labels, some just for filtering shit out of my way, and I don’t care at all how many unreads are in them.