Simple, reliable word truncation whether HTML exists in the text or not.

NSString+Truncation.h

@interface NSString (WordTruncation)
- (NSString *)substringOfHTMLToWordIndex:(NSUInteger)to appendOnTruncate:(NSString *)append softLimit:(int)leSoftLimit;
- (NSString *)substringToWordIndex:(NSUInteger)to;
@end

NSString+Truncation.m

@implementation NSString (WordTruncation)

- (NSString *)substringOfHTMLToWordIndex:(NSUInteger)to appendOnTruncate:(NSString *)append softLimit:(int)leSoftLimit
{
  if (to <= 0) return @"";
  
  static NSArray *htmlSinglets    = nil;
  static NSString *wordsRegex     = @"&[^;]*;|<[^<>]*>|(\\w[\\w-]*)",
                  *tagsRegex      = @"<(/)?([^ >]+?)(?: (/)| [^>]*?)?>";
  if (!htmlSinglets) htmlSinglets = [array_(@"br", @"col", @"link", @"base", @"img", 
                                            @"param", @"area", @"hr", @"input") retain];
  
  NSString *closingTag, *tagName, *selfClosing, *tag, *tail;
  NSUInteger i = 0, pos = 0, endTextPos = 0, words = 0, softEndTextPos = 0;
  NSMutableArray *openTags = [NSMutableArray array];
  NSRange match1, match2;
  NSString *copy = self;
  while (words <= (to + leSoftLimit)) {
    tail = [copy substringFromIndex:pos];
    match1 = [tail rangeOfRegex:wordsRegex capture:0];
    match2 = [tail rangeOfRegex:wordsRegex capture:1];
    pos += (match1.location + match1.length);
    if (match1.location == NSNotFound) break; // end of string
    tag = [tail substringWithRange:match1];
    if ([tag hasPrefix:@"&"] && [tag hasSuffix:@";"]) goto _continue; // entity
    if (match2.location != NSNotFound) { // real word
      words++;
      if (words == to) endTextPos = pos; // advance cursors
      if (words == (to + leSoftLimit)) softEndTextPos = pos;
      goto _continue;
    }
    closingTag = [tag stringByMatching:tagsRegex capture:0];
    selfClosing = [tag stringByMatching:tagsRegex capture:1];
    tagName = [[tag stringByMatching:tagsRegex capture:2] lowercaseString];
    if (selfClosing || [htmlSinglets containsObject:tagName]) { 
      // do jack shit if self closing or ignorable
    } else if (closingTag) {
      // check for match in open tags list
      i = [openTags indexOfObject:tagName];
      if (i != NSNotFound) { 
        // SGML: and end tag closes, back to the matching start tag
        // all intervening start tags with ommited end tags
        openTags = [[openTags objectsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:
                     NSMakeRange(i+1, [openTags count] - 1)]] mutableCopy];
      }
    } else { // add to start of open tags list
      [openTags insertObject:tagName atIndex:0];
    }
  _continue:
    closingTag = tagName = selfClosing = tag = nil;
    continue;
  }
  if (words <= to || (leSoftLimit > 0 && words <= leSoftLimit)) 
    return copy; // no truncation needed, take into account soft limit
  NSMutableString *ret = [[copy substringToIndex:endTextPos] mutableCopy];
  for (tag in openTags) { // close open tags
    [ret appendFormat:@"</%@>", tag];
  }
  if (append)
    [ret appendFormat:@"%@", append];
  return ret;
}

- (NSString *)substringToWordIndex:(NSUInteger)to
{
  NSArray *words = [self componentsSeparatedByRegex:@"\\s+"];
  if ([words count] > to) {
    words = [words objectsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:
                                     NSMakeRange(0, to)]];
  }
  return [words componentsJoinedByString:@" "];
}

@end