This pick tells me Romney is concerned about his credentials with the conservative base. That makes sense. You need to get your base out to vote. You can win over every single "swing vote" in the country and still lose if you don't get enough of your base support out.
Everyone else is going to give you the electoral ramifications that follow from this pick. I'll just say that in the end this probably won't matter that much. What I wanted to focus on is what this could mean down the road if Romney were to win the election. With Ryan as VP, I think this could mean a lot for Romney's legislative output. Most of that depends obviously on the structure of the House and Senate. Republicans will control the House. But it looks like Democrats may keep the Senate.
At worst Romney will probably have to work with a Republican House to send legislation to the Senate. I think this is significant because Paul Ryan is one of the leaders in the House. His budget is what Republicans tried to send to the Senate and Obama as their big response to Obama's election a few years earlier and their election in the midterms. So Ryan knows his way around the House and the House knows what Ryan is about.
With Ryan at the White House with Romney, I think it could be a hedge against Jimmy Carter-type battles that create gridlock and prevent legislation from getting passed. Aside from likely not creating friction between what congress and the president want to pass on a substantive front, this could also help them pass things quickly and capitalize on the so called honeymoon period after just being elected. This would put pressure on Democrats in the Senate to either accept gridlock by voting down legislation or to try and compromise in order to get things done.
If Republicans were to somehow take the Senate, it could mean that Romney and Republicans can try and match or surpass the rate at which Obama and Democrats passed legislation. That's important because Democrats took a lot of time to get the ACA drawn up and passed. And it could be argued that it cost them votes and popular opinion. It also very likely kept them from confronting other issues such as climate change.
Electorally I think the Ryan pick will be about a wash. It could help Romney secure his base. But it could also galvanize some independents and give liberals more to criticize Romney about. But if Romney were to win I think this pick could be significant in terms of actually governing. If this was a consideration of the Romney campaign then I give them credit for trying to think with some foresight. If it was purely about the election I it's probably not a bad pick.