No. It will however have an impact on the usabilitly and possibly even the accessibility of your Web site - that, and forcing links to open in new windows can royally tick people off.
I open links in new tabs (always) so if a site owner has made those links to work on parent window or new window for me it won't make difference. What Dan said tho it is pretty much true, many visitors would feel annoyed from getting new links open in new window and find their bar full of browser windows. (strange tho, my brother doesn't give a damn, he can open like 500 windows while he reads news online and non of them disturb him, i just watch and laugh).