I use two accessories that really improve the usefulness of my Pre 2. First, like many others, I have added an extended battery. It makes the phone thicker but I don't mind the girth because the longer operating time is worth it. I have also added a dual-sim adapter and that gives me benefit of two numbers on one device and how the Pre 2 handles it is quite elegant.
I use the Magic Sim No-Cut B adapter. I didn't want to damage my SIM in case it didn't work out the way I wanted to and the this form factor fits the second sim on top of the extended battery and underneath the battery case.
Both sim's don't operate at the same time but it is much easier than the sim swap I had to do previously. I have one sim on roaming and one sim local so I occassionally check my messages on my roaming sim and reply to them while keeping the same conversation history. Also, it is possible to use the SIM Toolkit of whatever sim is active.
The only downside is that switching the active sim too many times in succession will require a restart. I've ordered one for my Pre 3 and I hope it will work equally as well there.