Evaluating successive generations of HP’s TouchSmart series reminds us of shopping for a new car. If you fall in love and buy this year’s model, you must never, ever visit the showroom to look at next year’s model or you’ll be hit with a bout of buyer’s remorse faster than you can say “planned obsolescence.”We’re not suggesting that HP is intentionally designing these machines to have a shorter-than-normal useful life or that it’s been adding frivolous features to new models; it’s just that the company’s engineers keep making design improvements that are significant enough for us to wonder why we heaped such praise on the previous iteration. The changes this year are a wee bit more incremental, but HP gets a major assist from Microsoft in the form of Windows 7, which is not only vastly superior to Vista but also offers far better native support for HP’s touch applications. Fortunately, owners of previous-generation TouchSmarts have the option of upgrading to Windows 7 and downloading the latest version of HP’s software.But let’s get back to the matter at hand: Just what makes the TouchSmart 600-1055 so damned sweet? There’s the display, for starters. Last year’s model had a 22-inch display with a native resolution of 1680x1050; this one has a 23-inch screen with a native resolution of 1920x1080, making it the perfect partner for both the slot-feed Blu-ray drive and the integrated HDTV tuner.