With a couple of exceptions, most of my recent computer purchases (including laptops) have come with Ubuntu pre-installed. Because my time is valuable, I decided that I'd rather spend my free time not trying to determine why something wasn't working.
The advantage to buying an Ubuntu pre-installed laptop is you know everything works and is likely going to stay compatible regardless of future Ubuntu releases. Different Linux laptop vendors have various approaches to ensuring compatibility; the common approach has been to use PC hardware known to offer solid Linux support.
When selecting an Ubuntu pre-installed laptop, I recommend considering the following before jumping into a new purchase:
Not every model of Ubuntu laptop is going to meet everyone's needs, equally. Therefore I recommend following these guidelines when deciding which is best for you:
Blogger/writer – Same as above, although I would also point out that netbooks are also an option in this regard, since you're basically needing a laptop with minimal resources.
Gamer/Desktop replacement – With this example, power is everything. To date the most powerful Ubuntu pre-installed option is offered by a company called System76, and the laptop is called the Bonobo Extreme. Dedicated graphics, extremely powerful CPU options and a strong NVIDIA GPU puts this monster of a laptop ahead of the curve when compared to other models. Keep in mind that this model weighs in at eight and a half pounds, so this is indeed the laptop for someone looking to replace a full desktop PC.
Shopping for a new Ubuntu laptop can be a very personal experience. The decision process is often filled with angst and tense emotion, since there is often considerable investment taking place.
The thoughts and considerations I've shared above are based on many years of experience in dealing with Linux and installing Linux onto laptops, especially Ubuntu. Fact of the matter is, if easy is your goal – buy Ubuntu pre-installed. If instead, you're willing to take fate into your own hands or simply have extensive Ubuntu experience with hardware compatibility, then by all means buy the hardware that works best for you.