I am generally a fan of pair programming. Having said that, though, I rarely feel at a loss for good ideas on how to solve problems when I am working on small, incremental additions by myself. Making small, incremental changes is what most of us do most of the time. Often, I write code without any input from team members at all and do pretty well. Other times I will have a short discussion with other developers to discuss ideas and weigh options. For me, this seems to be enough to generate good code. Most of the work that I do without the input from a pair programmer seems to turn out well. So, I tend not to pair that often.
The only time I ever really feel any kind of despair while programming is when I am dealing with a tricky bug. When I am working on a change that breaks something unexpectedly I often feel a sense of panic. Something I have done has had an effect on another part of the system. Many times, I will not know a lot about the broken part of the system. This is when I feel a strong need to sit down with someone else who knows about it and talk through what I did and how it might have affected it. In fact, I often wish I had more than one additional person to talk to.
Of course, one might argue that if I had pair programmed with the 'right' person in the first place I wouldn't have made the error or felt the panic. However, it is difficult to anticipate what is going to go wrong and, therefore, who to pair with. So, at least for me, I don't feel like pair programming all of the time is the best use of my partner's time. I feel like having short discussions with my team members and pair debugging on demand is the most effective for me.
I am all for pairing when I don't have a good, strong idea on how to solve a problem or either I lack some experience or my partner does. I like to pair when I am learning a new system or subsystem. I also choose to pair in the very early stages of a system's development when everything is brand new and just being built.
Mostly, though, I like how knowledge spreads from more informed developers to less experienced ones. I don't insist that every single line of code be written in a pair for my projects. I tend to use pair programming as a learning tool more than a creativity tool. I feel it is most valuable when I know I am lacking some knowledge, that is, after I have broken something and can't figure out how to fix it.