Using the keyboard is one of the things that Palm got mostly right with the Pre. It's a good sized keyboard, easy to use one-handed, and easy to open and close one handed as well.
The keyboard has a natural feel to it, and it was fairly easy to adjust to from a standard keyboard of this size and shape. The rubberized keys were a bit of a surprise, but haven't had any problems with them, and it seems to keep gunk from getting inside them. The matte black rubberized finish is also a nice contrast to the white keys and orange 'alt' keys, and helps to make the keys stand out when backlit.
I find texting/IMing and entering text as a whole to be mostly pretty easy. The CAPS, Alt and 'Symbol' functions are easy and obvious, and a cursor indicator lets you know when you're in a 'onetime' or permenant mode (meaning every time you type, it's either caps or 'Alt', depending on what you've selected).
The only complaint that I have about entering text in the Pre is the lack of an ability to scroll or move the cursor within a text field. If I mis-type something and need to correct it, the only way for me to do it is to either delete all the way back to the place where I mistyped, or try my luck with touching the exact spot that I need to correct. Given that the pre is designed for finger gestures, not fingernail gestures, this level of accuracy seems nearly impossible to achieve. I don't believe I've ever gotten the cursor where I want on the first try. More often than not, it takes 3 or more attempts to place the cursor where I want it. The only thing which seems to improve accuracy is if you happen to be on a website, you can zoom in really close to the field so it's larger and you have a better shot of getting the curson in the right place. A scroll ball (like on the G1) probably isn't realistic for the Pre (although it seems the white round button would have been a good candidate for this), but some sort of ability to move a cursor backwards and forwards would have been great.
Alas... this is the only complaint I can find with the keyboard, so I'll just learn to be a better thumb-typist.