Oversized Delete key = fail.
Most Logitech keyboards have an "oversized" Delete key. I find it actually really nice, cause it's possible to just slam the Delete button if you're really in the mood to free up HDD space
I think it's just a question of habits.
I think I could put in my experience as well: Logitech S 510. Nothing else needs to be said. The keyboard is awesome, with small media buttons on each side plus the normal F1-F12 keys can be swapped to function as hot keys for launching applications or do other stuff like print the page, etc... The placement for Home, End, Page Up and Page Down buttons are awesome and logical. The over sized Delete is a great plus as well. Overall typing feels very smooth and fast and the keyboard is pretty silent (after use though the keyboard starts making more noise, unless you type every time very gently). The mouse is similar to Logitech LX5 and is quite fast in moving the cursor on the screen. The mouse doesn't feel as comfortable as Logitech's more expensive products, but is big enough to fit well (just like GameCube controllers fit well, not too small like PlayStation 2 controllers and not too big like the XBOX 360 controller). I once tried to do the smooth scrolling mod to the mouse but it was not possible. When trying to lift the plastic casing of the mouse it forces you to break the front part (it's like soldered in). I ended up shorting my mouse, but luckily got a new set (just said the mouse "suddenly" started to feel warmer and my batteries nearly exploded for no reason when I was at the local PC store
Overall the Logitech S 510 is awesome! Be sure to get the version with the included Media Remote so you won't need to sacrifice a USB port for an infrared receiver.