From the question, it sounds like the ly ending will fit nice.ly with their site. Quite like.ly even.
Yes - seen this quite a few times one that worked really well was countly which bought count.ly nice and easy to remember.
I think if it forms part of the brand / name then these domains whilst vanity are really memorable. Its not quite the same impression that I get when someone just registers mywebsite.ly which looks like you are just uber cheap!
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