TweetDecoder.cs

    public enum TweetSectionType { NormalText, Url, AtName, HashCode }

    public class TweetSection
    {
        public TweetSectionType SectionType;
        public string Text;
    }

    public class TweetDecoder
    {
        #region regex patterns
        
        // strict match - won't allow for stuff before the @
        public const string atRegexPattern = @"^@([A-Za-z0-9_]+)$";

        // strict match - won't allow for stuff before the #
        public const string hashRegexPattern = @"^#([A-Za-z0-9_]+)$";

        // here be dragons - this is a loose url match
        public const string urlRegexDragonPattern = @"^((https?|ftp)\:(\/\/)|(file\:\/{2,3}))?(((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))|(((([a-zA-Z0-9]+)(\.)?)+?)(\.)([a-z]{2}|com|org|net|gov|mil|biz|info|mobi|name|aero|jobs|museum))([\/][\/a-zA-Z0-9\.]*)*?([\/]?(([\?][a-zA-Z0-9]+[\=][a-zA-Z0-9\%\(\)]*)([\&][a-zA-Z0-9]+[\=][a-zA-Z0-9\%\(\)]*)*?))?$";

        #endregion

        #region regexes

        // always the same so declare once as compiled for faster execution
        private static Regex atRegex = new Regex(atRegexPattern, RegexOptions.Compiled);
        private static Regex hashRegex = new Regex(hashRegexPattern, RegexOptions.Compiled);
        private static Regex urlRegex = new Regex(urlRegexDragonPattern, RegexOptions.Compiled);

        #endregion

        // Here be magic.
        public static List<TweetSection> DecodeSections(string originalTweet)
        {
            // declare return variable
            var sectionz = new List<TweetSection>();

            // split in words
            var wordz = new List<string>(originalTweet.Split(' '));

            // loop through words and figure out what kind of section.
            foreach (var word in wordz)
            {
                // section defaults to normal text
                var sectionType = TweetSectionType.NormalText;

                if (atRegex.IsMatch(word))
                {
                    sectionType = TweetSectionType.AtName;
                }
                else if (hashRegex.IsMatch(word))
                {
                    sectionType = TweetSectionType.HashCode;
                }
                else if (urlRegex.IsMatch(word))
                {
                    sectionType = TweetSectionType.Url;
                }

                // add word to section list or append to last if they're both normal text
                if (sectionz.Count > 0 
                    && sectionType == TweetSectionType.NormalText
                    && sectionz[sectionz.Count - 1].SectionType == TweetSectionType.NormalText)
                {
                    sectionz[sectionz.Count - 1].Text += ' ' + word;
                }
                else
                {
                    sectionz.Add(new TweetSection { SectionType = sectionType, Text = word });
                }
            }

            return sectionz;
        }
    }

Yep - in the end if your decoder works and you're happy enough I don't see a need to replace it!

Might wanna look into HttpModules as an alternative to global.asax, global error handling example here --> http://bit.ly/dgrt6k (accessing HttpContext in the example) - also see here (SO question) --> http://bit.ly/b9akSs

Thanks for your input. I'm totally rocking the HttpModules at the mo'. The main handler at the mo' is the HTML one twipler.com/timeline.html is a dynamic response.