Thank you, I guess
You've received thank-you notes yourself. The ones that say, “Thank you for your generous gift!” probably raise a flag in your mind. “This person wrote the same thing to the 128 other people at that wedding,” you think. And you're probably correct.

Writing generic thank-yous saves time and brainpower; you've probably written them yourself once or twice. However, to the reader, it is unlikely that this kind of note portrays more than just a formality. Being general in your note is a quick way to turn off the reader… the same person who was kind enough to give you his money/time/thoughtfulness.

Other things you should avoid doing are: asking where the gift was purchased (if you have a return/exchange in mind, keep it to yourself!); telling the person if you received duplicates of the gift he gave you (don't make a guy feel unoriginal); waiting months since the gift was delivered to thank the person; including other information about yourself and your life in the note (save that for a personal letter); and over-stating your thanks (saying things like “You are a lifesaver!” if all he did was let you borrow his vacuum).