Summary: Greatly improved over the 2004 edition, which I thought was rather poor compared to most Lonely Planet (LP) guides. LP has a consistent format among its guides, making it easy to use if you are familiar with another LP guide, and it has some of the best listings for details you need to know before and during travel.
The two leading guidebooks for Taiwan at time of writing are Lonely Planet Taiwan (LPT) 2011, and Rough Guide Taiwan (RGT) 2011. Each has its pluses and minuses. RGT used to be better than LPT, but the LPT guide has been improved. I suggest you peruse both at your local library and decide which style works best for you.
Taiwan is a fascinating but underrated set of islands, with friendly and helpful people, many of whom speak at least a little English or Japanese. The Chinese culture here is fascinating, but I had no idea before I came here the first time that there were people other than those descended from the Chinese. The indigineous Austranesian peoples add ethnic cultures, arts, and cuisines to get to know.
The diversity of natural beauty on this island is staggering - mountains, rugged coastline, waterfalls, and unique wonders like Toroko Gorge. You can see it all easily because of the new high-speed bullet trains that can take you from Taipei to the south in just over 2 hours. (Buses from the train to inland areas are not as fast, of course.)
Even if you have to stay in Taipei for work reasons, there are many day trips to enjoy; Wulai is easy and worthwhile, and you could even take a train to see a little of the south, yet return the same day.
PROS
Predictable LP layout makes it easy to find what you need quickly, especially if you are used to the LP layout from using other LP guides. LP guides always have the essential travelers sections that make them very useful.
The overview section at the front focuses on helping you decide where to go, and build an itinerary based on your interests.
Smaller fonts (compared to RGT) means more information on fewer pages, but is also a CON for middle-aged eyes.
The incomplete and erroneous coverage of tea from LPT 2004 - and tea is fundamental to Chinese culture - has been replaced with more and more accurate information.
CONS
The Table of Contents is on pages 38-39 (!), rather than at the beginning where I expected to find it, and it only covers the regional sections. For the overview sections and appendices, you will need to rely on the index.
Fewer pages used to describe each region of Taiwan, compared to RGT 2011. No separate section on Central Taiwan.
Only five pages on Mandarin Chinese. I would have liked to see at least a basic vocabulary for Taiwanese dialect and the most common aboriginal languages, because even just basic greetings in your host's native language builds good will.
Some LP guides have a map section, in addition to local maps in the regional section. This one does not.
Many names are written both in Roman characters and in Chinese characters, though some maps are missing the Chinese characters.
CONTENT AND ORGANIZATION
Overview - 38 pages - highlights, suggested itineraries, basic information
Taipei - 67 pages
Northern Taiwan - 48 pages
East Coast and Taroko Natl Park - 36 pages
Western Taiwan and Yushan Natl Park - 40 pages
Southern Taiwan - 41 pages
Taiwan's Islands - 38 pages
Understand Taiwan (History, People, Culture, Cuisine, Wildlife, Language, etc) and Index - 94 pages
Total: 404 pages
OTHER COMMENTS
While many Taiwanese speak at least some English, and many younger or more-educated people can speak it reasonably well, you will at times need to look at the Chinese characters to find things (like the bus I mentioned in Cons). Unfortunately there are two or three different English spelling schemes used for Chinese words, so you will need fuzzy thinking using sounds in your head to work it out. Example: Xindian (the MRT spelling) is spelled Sindian on the buses. A road like Zhongshan might be spelled Jhongshian or Song Shan, but Songjiang is a different road in the same area.
Another reviewer panned this book because of "inaccurate" spellings in the guide. On page 381, the author discusses the problems caused by multiple methods of writing Chinese in Roman characters, and points out that for in this guide they use Hanyu Pinyin along with Mandarin Script. Hanyu spelling won't always match what you see, and that is confusing, but from my perspective, the problem is the lack of standards in Taiwan, not LPT errors.
BTW, I have found that some Taiwanese can also speak some Japanese.
WHO, ME?
I have spent a lot of time all over Asia and have visited Taiwan about five times from 2001-2010, mostly Taipei for business, but I have taken some time to visit other parts. I have used LPT 2004 and RGT 2007 during these trips.