If you're only running the script a few times a day then it's unlikely anything will actually go wrong. The main issue are as follows:
- You need to supply a dummy useragent similar to one produced by a browser
- Search results vary depending on factors such as the IP you're using so you might not get results that are as useful as they seem
- Google regularly changes the way they display results and it could break your code so it needs to be updated
Google terms what you are doing "Screen Scraping" and this is against their usage terms of service no matter how few times the script is run. They state that this is because it puts excessive loads on their servers.
However, I think that there's probably a copyright issue as well. If they let people easily copy their content then it would be possible to create a very cheap search engine that takes results from Google but replaces the ads. Google spends a lot of money on their search algorithm and needs to collect ad revenues to make a profit and continue development.
I guess that they also don't want marketers running these types of script because they don't want SEO's trying to gain insights they can use the unfairly manipulate rankings. There might be a similar issue for AdWords where they don't want marketers knowing too much about the keywords and ads that their competitors are using.
The main defense that Google uses against automated scripts is to temporarily block IP's that issue too many requests within a short period of time. As I stated earlier, your script shouldn't run into this problem but people issuing large numbers of queries usually use proxy servers to make regular IP changes and reduce the chance of detection.
Finally, this is beyond the scope of the question but another issue this type of script faces is that they also violate the terms of service of other Google systems. For example, the AdWords API TOS explicitly states you can't use the API with such a program. This could lead to API Developer Tokens being revoked on detection of these methods.