I have a home theater PC (HTPC) and have spent a lot of time trying to find an ideal means to control it. While there are a lot of options available on the market, almost all of them fall short in some area.
I have tried quite a few cordless peripherals that all used the standard RF interface via USB dongle. These devices utilize the already crowded 2.4 Ghz frequency band, which you may recognize as the same frequency used by Wifi, many cordless phones and baby monitors. All this interference from other devices means you will have a lot of problems with dropped signals, missed clicks, etc.
Furthermore, optical mice really suck to use on your lap, so I knew I would need something a little out-of-the-ordinary. I have tried a Gyration Air Mouse, which was really neat, but it used an RF dongle and suffered from the aforementioned signal dropouts. :-( Furthermore, the Air Mouse is a delicate piece of machinery with several gyroscopes inside that can get out of alignment if the device is dropped a few times, which is almost unavoidable if you place it on the arm of your couch or chair.
Based on these experiences, my requirements are: Bluetooth, integrated cursor control and Linux support (since I use Ubuntu for my media center). Now, you would think that this sort of thing would be easy to come by and that there would be hundreds of options to choose from among a variety of vendors, but this is simply not the case. In my experience, there are only two viable options: the Logitech Cordless MediaBoard Pro and the Logitech diNovo Mini.
While the diNovo Mini is very cool, it is expensive (approx. $120 at the writing of this review) and the keyboard is of a strangely awkward size that makes it slightly too large for thumb typing but far too small for touch-typing. Additionally, its trackpad thingie in the upper-right takes some getting used to. On the plus side, it's small enough to fit into couch-side storage along with regular TV remotes or even in your pocket. It also has an integrated, clamshell cover that nicely covers the keys when not in use.
However, the small keyboard and funky trackpad thingie make it unsatisfactory for general computing, such as Web browsing and typing, in my opinion.
In contrast, the MediaBoard Pro is much cheaper (approx. $60 currently), but it is marketed for the Playstation 3 rather than for standard PC use. Do not let this scare you away. It syncs fine with both Windows and Linux via the standard Bluetooth stacks with minimal fuss (notice: Logitech also makes a non-Pro MediaBoard that uses 2.4 Ghz RF; make sure you don't buy it on accident) and the PS3-specific media keys can be easily ignored or repurposed with key-mapping software.
The MediaBoard Pro is a full-sized keyboard with all of the keys you would expect, including F-keys, Del/Ins/Home/PgDwn/PgUp/End keys, etc. The only key that is missing is the Windows key, which has been replaced by dedicated keys for left- and right-clicking. It also has an integrated trackpad--similar to those found on most laptops--off to the right, where the keypad would normally be located.
I found the trackpad to be responsive, if a bit on the small side, and it has an area on the right side that is dedicated to scrolling (similar to the mouse wheel) and worked quite well without any configuring.
Some minor quibbles: this keyboard feels very light and somewhat cheaply made, but I guess that's what you get for $60. Also, it has a glossy black finish which looks really nice at first but attracts fingerprints and tiny scratches like nobody's business. Lastly, I have a feeling that the silver finish on the accents will quickly rub off, likely leaving an unsightly unfinished plastic instead.
All in all, I think the Logitech Cordless MediaBoard Pro is the best option for anyone who plans to do any actual computing (typing, navigating, Web browsing, etc.) with their HTPC. If you intend to use a media frontend, such as MythTV or XBMC, the diNovo Mini might be a better fit, since it feels more like a conventional remote and those interfaces do not require as much mouse/keyboard action.