For years the main reason I had a bottle of vermouth to hand was principally for cooking with, generally Noilly Prat or Dolin Vermouth de Chambéry. Both are dry vermouth's, and I'd happily substitute either into a recipe that called for dry sherry, Marsala, or even dry white wine. They're not interchangeable, but they have enough in common not to be totally incongruous when they're swapped around. I'm certainly not going to open a bottle of dry sherry if I've got Vermouth on the go and vice versa.
Partly because I saw it primarily as a useful ingredient, but also because of an occasional prejudice against sweeter drinks, I sort of assumed I would only like dry white vermouth which meant years of missing out on the Rosso's which it turns out I love - but have a different role in the kitchen.
It's a dry French vermouth that would go into a classic sort of Martini, it also works really well with tonic water and a wedge of lemon for a lighter alternative to gin and tonic. It's worth trying with soda water if you want to reduce the sugar content as well as the alcohol. It's pretty good neat too - Jack Bevan recommends Nocellara olives and a slice of lemon on the side with Noilly Prat.
Again, before reading 'A Spirited Guide to Vermouth' I hadn't considered drinking it with tonic or soda as a long drink, but it was a happy discovery. The perfect spritzy drink for the cook who forgets vital ingredients half way down a G&T, and can't be trusted with a sharp knife by the 3/4 mark (which would be me).
I'm currently playing around with a bottle of Belsazer's summer edition reisling based vermouth (it has a pineapple flavour which makes it unlike anything I've ever encountered before. It's a sweeter Vermouth than I'd normally buy (this is down to 'A Spirited Guide...' as well, it sounded so intriguing it was the one bottle I had to try). I think it would be excellent instead of Sherry in a trifle - its flavour profile would add something really interesting, so that might be a plan for the end of the bottle.
Diana Henry talks a bit about how chicken loves alcohol in 'A Bird in the Hand' and how we haven't really been in the habit of considering alcohol as a store cupboard staple for cooking with. We probably should though. It's an easy and quick way of making a simple, in this book chicken, dish into something luxurious (she gives an excellent set of guidelines for this). A good dry vermouth is just as handy when it comes to fish, and has its place with pork too. If a bottle wants finishing (but before it's gone to far over it's best - if you wouldn't drink it with pleasure don't cook with it) There are worse places for it to end up in than a gravy.