One is that we've already seen that in a contest with little solid support for any candidate, very large short-term surges are likely. Even Herman Cain had a bit of one, and Donald Trump had a huge and entirely meaningless one. Perry isn't Cain, and he certainly isn't Trump; he's a very serious contender who might well win. But at least part of this polling surge may well dissipate in the next few weeks, as his announcement bounce fades. It's impossible right now to know how much of his polling support is real and how much is fluff.
The other is that running for president is hard, and he hasn't really done much of it yet. Paul Waldman has a good post today on that, focusing on talking to the press:
[E]ventually, Perry will have to do an interview or two. The reporter will prepare some tough questions. And, I predict, it won’t go well for Perry.Who knows? Perry might nail it. He's not inexperienced, although Waldman is right that Perry is entering a very new environment. But it's not just the press. There are also debates, and campaign management, and dealing with whatever will be dug up about his past.
It's also about dealing with setbacks in the full glare of press attention. Lots of people win elections, especially primary elections, without encountering real trouble along the way. No one wins a presidential nomination without some very bad days. Moreover, during general election campaigns a nominee has an entire party with a strong interest (and probably an emotional investment) in rallying around her. Not so in nomination struggles.
I'm not predicting that Perry will fall flat -- indeed, I think that the odds are that Perry or Romney will be the nominee -- but I do think that some good polling numbers right after his announcement shouldn't be taken at face value. Long way to go.