Below is a letter from the U.S. Department of State very clearly stating that U.S. citizens need to remember Thailand's new enforcement of the government's visa exemption policy. At best, the border run days are over. At worst, even those with tourist visas might be limited. I have read of several people being denied tourist visas because they've already spent 90 days in the country. As was the case in the past, tourists are allowed 90 days in the country out of 180 days. Thus, if you have a single entry tourist visa, there is a chance the Thai embassy will not issue a second visa for another 90 days. If you have a multiple entry visa, you should have no problems. Should being the key word.
Thai Immigration’s Enforcement of Thai Visa Exemption Policy
July 7, 2014
U.S. citizens are reminded that Thailand immigration laws require visitors to remain in the proper visa status. U.S. citizen tourists traveling to Thailand are eligible to enter Thailand without a visa and stay for 30 days under the Thai visa exemption policy if they are able to show an onward/return ticket and possess a passport that is valid for at least six months beyond their date of entry into Thailand.
The Thai Ministry of Foreign Affairs has informed us that Thai Immigration will enforce existing foreign entry regulations and step up efforts to prevent abuse of the 30-day visa exemption policy for tourism granted to some foreigners, including U.S. citizens. Thai immigration authorities will review carefully travelers who have received permission to stay for 30 days through the visa exemption policy, and who subsequently seek to reenter Thailand repeatedly for an additional 30 days under the same program. If immigration officials perceive that individuals are entering Thailand to reside for an extended time or indefinitely, rather than seeking entry for tourism, such individuals may be denied re-entry. If so, they will be referred to a Royal Thai Embassy outside of Thailand to apply for a regular Thai visa before seeking to enter Thailand again. The U.S. Embassy and Consulate are not able to intervene with Thai Immigration or the airlines regarding their regulations and policies on behalf of a U.S. citizen who is denied re-entry.
U.S. long-term tourists and business travelers should check with the Royal Thai Embassy about Thailand’s visa requirements. Additional information is available at the Department of State’s Country Specific Information for Thailand at http://travel.state.gov/content/passports/english/country/thailand.html.