Having looked at the example skin Ralph Williams provided I discovered that the same inline style appears there.  Further investigation led me to discover that this inline style is added by the javascript in the dnnmenu control .js file.  By setting ControlOrientation="Vertical" as a parameter to the NAV control I came around that problem.

However, the more I investigate, the more I am convinced that the default menu provider is, to my approach, broken.  Or, it works at what it does but it is built on a faulty premise.  The fault is that way too much is done with javascript, completely unnecessarily.  For example, all the useful classes for CSS styling of the menu (those which indicate the level in the menu, the breadcrumb trail, etc.) are added to the items after rendering the page, using javascript.  I really fail to see any advantage to this - why are they are not added when the list itself is rendered?  A menu is the most basic navigational tool on a website, and there is very little which cannot be done with CSS.  In my opinion the basic navigational tools on a website should not be dependent on scripting - and nothing should be dependent on scripting which is just as easy to do when rendering the page.

Whatever, it doesn't work for me.  The script also takes the <ul> elements containing sub-menus out of the relevant <li> and puts them after the main <ul> element with a calculate absolute position.  I want a menu starting at level 2 (or, technically level 3 in that I'm using the localisation extension from Adequation).  As such I want to be able to hide all at level 1 and all at level 2 except children of the level1 breadcrumb.  Easy with the initial <ul> structure (if you have the breadcrumb, etc. classes), much more difficult with the one after javascript has messed with it. 

Anyway, as I said, I don't want to be dependent on javascript - it never occurred to me the classes would be added with javascript.  I'll investigate the DNNGarden solution instead.

Thanks for the helpful comments.  I'm not meaning to rant at you guys :)

Just wanted to say thanks to all who replied to this thread.  Especially to Mark Allan - I ended up using his DDRMenu instead of the standard menu.  IMO this is what the standard menu should be - it's a backwardly-compatible drop-in replacement but it's extensible allowing the skin designer to customise the menu as they will.  (Actually, I think the standard menu should use actual links instead of postbacks as I've already explained, but I understand if, for backwards compatibility, the default replacement is a straight copy of the output of the standard menu for now)