When I watched "First Contact" my impression was, that in the end, our heroes repaired the damage the Borg did to the timeline. But there were so many subtle and not so subtle changes, one could ask if there was really no impact on the timeline as we know it from TNG.
As answered in this question it is highly doubtfull that the Borg entcounters were unrecorded (and the following Borg events in Enterprise also) up to the TNG era and that the actions of our heroes in the past with Cochrane were completely without any impact on the timeline.
But if the timeline changed, what about the events in "Q Who" were the premise that the humans never met the Borg before is no longer true (and Q should know)?
So what impact did "First Contact" have on the TNG timeline as we know it?
Remember that after the first borg encounters (original timeline) the federation build stronger war ships like the Defiant (DS9/First Contact) to prepare for them. If there was a similiar effect after the events in "Enterprise", even the TOS era should have been completely changed (like in the reboot timeline).