Field guides are not tabboo as far as I'm concerned. The only reason I don't carry one is the same reason I don't normally carry a scope, i.e. I can't be bothered carrying them, because I don't use them enough.
I'm by no means an expert, but most of my birding is at my local patch which I visit almost daily throughout the year, and have done for nearly 20 years. This means that I know before I get there 99% of what I am likely to see. I see a new bird at my local patch maybe once every two years, and even then they're not always that difficult to identify. For example, in February I recorded my first Long-tailed Duck at the mere. I knew instantly what it was, I've seen hundreds before elsewhere, so no need for a look in a field guide.
You could argue that the field guide would help me age / sex the bird, but then which field guide would I take? Usually I find that no one guide is good enough. If I see a bird I'm not familiar with, I often refer to several guides, back issues of British Birds and the internet. Small pocket guides are ok when your a beginner and looking for your first Brambling or Grey Wagtail, but when you've been seeing those sort of birds for years, you don't need to look in a guide to id them. The sort of birds I need a guide for are the more obscure species such as leaf warblers and Calidris Waders, and in my experience pocket guides are next to useless for these species. Having said that I do have a brilliant pocket sized guide which I think might be out of print now called "The MacMillan guide", which soley concentrates of identifying difficult species, and completely ignores commoner and easy to identify species.
But none of this would stop me carrying a field guide, except that because of what I have explained above, I wouldn't know which one to take, and probably I'd have to take more than one, just on the off chance that today might actually be the day when I see something different. That sounds too much like hard work to me! I prefer to risk it and if I do see something different, take a few notes to refer to at home, and maybe go home for the scope and the books hoping that the bird stays where it is.
Colin