gistfile1.cs

using System;
using System.Diagnostics;
using System.Text.RegularExpressions;

namespace ConsoleApplication1
{
	class Program
	{
		static void Main(string[] args)
		{
			// http://d.hatena.ne.jp/n_shuyo/touch/20111020/regular_expression
			var pattern = @"[-_.0-9A-Za-z]+@[-_0-9A-Za-z]+[-_.0-9A-Za-z]+";
			var reg = new Regex(pattern, RegexOptions.IgnoreCase | RegexOptions.CultureInvariant | RegexOptions.IgnorePatternWhitespace | RegexOptions.Compiled);

			string dummy = repeat("abcdefg", 2000);

			Stopwatch sw = new Stopwatch();

			sw.Start();
			Console.WriteLine(reg.IsMatch(dummy));
			sw.Stop();
			Console.WriteLine(sw.Elapsed);
			Console.ReadKey();

		}
		public static String repeat(String st, int c)
		{
			string buf = "";
			for (int i = 0; i < c; ++i) buf += st;
			return buf;
		}
	}
}