I've always thought of flash as pretty much essential for indoor shooting, especially in dim/poor lighting.

But I went to visit a photographer for my sister's wedding this morning and some of his pictures were awesome. About two or three were formal posed pics, but the rest were just natural, spur of the moments and were simply awesome. He had to use his flash in two indoor pics but with the rest, he just used what was around him to ensure adequate lighting eg getting people to stand near the stage/wall light etc

So other than skill and experimentation, is there any way you can guestimate whether you need a flash, or whether you should use say a higher ISO?

I'm still trying to get the basics right but sometimes messing about with other things can break things up a bit and make learning photography more easy.

I don't "do" flash if I can avoid it. I try to use natural light whenever.

I guess the wedding photographer had the benefit of a nice fast lens (ƒ/2.8 or brighter) so he could capture in relatively low light. For candid work like that I'd probably be using a 35mm or 50mm, almost wide open, at about ISO800 or perhaps higher to keep a reasonable shutter speed for handheld work. Many recent DSLRs have excellent noise reduction, enhanced further by post-processing.

I keep pondering whether to add a separate flash to my kit, but if I'm honest it won't be used, and even if it was used it wouldn't be used properly.

I'll pretty much echo what Heather's said, so I won't repeat it other than to say that for the kind of work I do in dimly lit clubs and venues, I generally stick to ISO 800, ƒ/4, and generally get away with a shutter speed of about 1/10th of a second. I'm not anti a little movement, because I'm trying to capture a performance and I think that's how we remember things rather than a static. Also I feel it's a distraction for the audience and the performer to have me popping flashes every few seconds.

Anyway, however, there have equally been times when I've been shooting a wedding or a birthday party when a flash would've possibly taken an adequate shot up to a great shot had it been used correctly.
Comparing shots I took at a recent wedding (as a guest) with the professionally taken ones, he's maybe a little sharper than I am (but then he was using a £four-figure lens) in some places. He'll get away with a greater depth of field sometimes.

I think, ultimately, it's a stylistic choice that you make. Personally, I'm not a fan of it for performance or a more documentary style (like the examples you saw at the photographers) but in some instances, I think it can be appropriate.
Thinking about it, it feels like when someone's making a statement outside a court or something, there isn't the storm of flash bulbs we used to have 10 years ago.
Which of course makes me wonder if flash use might become a dying art.

Wow. I just used those settings on my G12 (with flash off and on aperture priority) and was able to pick up objects that I couldn't see with the naked eye!

White coloured objects were very bright though. Guess this is down to camera processing?

Exactly. Just experiment. I don't own a camera flash and my camera doesn't have an in-built one either. I've never used a flash for any of the pictures I've taken with my DSLR. There's been one time when experimenting with high speed photography that I could've used one, but I haven't tried that again since, so buying one for that would've been a waste.
I'm perfectly happy to stay away from taking flash photography.
Obviously I don't sneer at the people that do use it, it's just not for me.
I do have, for the most part, very fast glass though.
Just experiment with ISO and shutter speeds and I'm pretty sure that you'll be able to find a very happy medium that gets you the results you want.

Mark

I like to think there's a time and a place. Trying to take photos on an evening indoors of my baby baby most definitely required a flash. It also enabled me on a couple of occasions to take a nice photo against a white background - like they do in the studio. If I could do without it though I would.