I've been using the old (silver) wireless version of this keyboard on my Media Centre PC. It has finally died after giving me great service for a long time. Having run a USB cable to a powered hub next to my chair, I decided a wired keyboard would be OK as replacement.
First impression of the ACK-540U+ keyboard is that the key action is nowhere near as sweet as the old model. The travel is greater and they are clunky and noisy in use (would drive me mad on my main PC). The key layout is also slightly different in that the keys either side of the spacebar, and the Arrow keys, are 3/4 size. The Delete key has moved from the top right to being one of the 3/4 size keys and is placed next to the Left-Arrow key. This leads to the occasional delete when navigating the cursor via the Arrow keys. At first I thought there was no AltGr key, but the Right Alt key does the same function (useful for keyboard shortcuts), and there is no Right Control key. Having said the key layout is slightly different, I should point out it is a standard UK QWERTY keyboard with UK Pound key and Euro symbol is, as usual in Win XP onwards, available via the AltGr+4 (Right Alt+4) key combination.
The touchpad is a great improvement over the old one. Although it's slightly smaller than the old touchpad, it doesn't have the vertical scroll section down the right-hand side. It was way too easy to accidentally scroll a page when moving the pointer before. The multi-touch functions work well... single finger tap for Left-Click, two fingers for scrolling, three finger tap for Right-Click. The three finger tap appears to work like Middle-Click when used on a link in most web browsers (like Control/Left-Click), ie it opens the link in a new tab.
The LEDs for Num, Caps, and Scroll Lock is a welcome addition, although given my old keyboard was wireless and very battery hungry, it would not have been welcome on that keyboard.
As a small all-in-one keyboard/touchpad for use with a Media Centre setup this is a great product, only let down by the clunkiness of the keys. However I do far less typing on the Media Centre PC than I do on my main PC (I would not want this as my main PC keyboad). The addition of a set of Media keys would have made this the perfect Media Centre keyboard, but everything can be controlled via keyboard/touchpad, so I'm just being lazy and wishful.
For the purpose this was bought it gets 4 stars from me, would have been 5 if the key action was as sweet as my old wireless Keysonic.