Personally, I use 3 spaces for block indentation. The majority of Perl code I've seen has used either 4 spaces or some aweful combination of varying indentation. I just prefer 3 spaces because it shows the level of indentation just as well as 4 spaces, but requires that one less keystroke per indentation. I honestly don't see how people can stand using 8 spaces (not to be confused with an 8 space tabstop). I could not see myself banging in an additional 8 spacebar presses every time I enter a new block, as by the time you're in a 4th level block, you're punching in 32 spaces for each line of code and taking up 40% of the screen width (assuming 80 character width terminal) just for the whitespace. I have to wonder if there aren't code samples out there that use 8-space indentation that contain more whitespace characters than non-whitespace ones. Talk about a waste of bandwidth and storage space.

As for using tabs rather than spaces, I despise that all to hell. Tabs are even worse than 8 space indentation because of cross-editor type behaviour. Ugh! Who invented the damn tab key anyhow? It should be deprecated, except for tabbing between window elements :)