Are there stealth boy side effects?

No, the effects of long-term Stealth Boy abuse, both positive and negative, as seen in the Nightkin will not manifest for the Courier in Fallout: New Vegas.

This is confirmed by Doctor Henry in Jacobstown, if asked, he informs the Courier that he has never seen Nightkin-style Stealth-boy-schizophrenia manifest itself in a human.

I don't have a definitive answer for New Vegas, but in all the other Fallout games the stealth boys have no negative effects. Additionally, in terms of gameplay, any "negative" effects they might have will mostly likely be a net positive for a player as they will manifest as a perk.