To some people it is - but it can be incredibly effective when looking to build relationships that could lead to business.
I first posted this blog in 2013, and whilst LinkedIn have improved the Skills functionality, I still recommend the advice in the piece.
In fact I do that because I've had clients tell me that the very first time they said 'thank you' on LinkedIn, it resulted in them attracting a valuable new customer.
I recently suggested that when someone looks at your LinkedIn profile, you take the trouble to thank them. One or two people got in touch with me to suggest this was "groundbreaking advice" and that thanking people was the last thing on their mind. Yet to me it's a common courtesy surely?