From the Washington Post:

Before the announcement, senior citizens split 28 percent apiece positively and negatively on Ryan, but afterward his favorable number shot to 46 percent with no change on the other side of the equation. Seniors are likely to get even more outsized attention in the coming months due to Ryan’s controversial proposal to change the Medicare entitlement. A Post-Kaiser poll released over the weekend shows broad, cross-party opposition to such a change.

More data from the poll:

Overall, in interviews after his selection, 38 percent of all Americans express favorable views of Ryan, 33 percent negative ones. (Before the the announcement, Ryan was somewhat underwater, scoring 23 percent favorable, 32 unfavorable.) The most recent national numbers on Vice President Joe Biden are from a July Pew Research Center poll showing a split decision, 40 percent favorable, 37 percent unfavorable.
One of the largest movements on Ryan’s favorability numbers was the 21-point jump among conservative Republicans, but the initial movement was positive among independents as well, doubling from 19 to 39 percent. The shift among Democrats was similar in both a positive (up 10 percentage points on favorability) and negative direction (up eight on unfavorability).

It’s early days, and the Obama campaign is going to be working feverishly hard to define Ryan as the guy who wants to leave senior citizens impoverished and on the street, begging for medical care. But these numbers show that so far, such impressions haven’t sunk in for most Americans — and if Ryan can remain on the offense (and defend himself eloquently from the charges of trying to hurt seniors), he has decent odds of escaping being caricatured nationally as some heartless, benefits-slashing monster.