The mechanic in my local bike shop reckons 29ers are not suitable for anyone under 6ft.
The front end is very high, exaggerated when a 29er fork is bolted to a small frame.
I posted this in Scotia's original what bike? thread, and while there is smug satisfaction in being proved right, I'm sorry she's had to mess around changing the bike.
Just to re-iterate, I am nearly 6ft and have a small framed Rose 29er trekking bike - the front end is a shade too high for me.
I think the height problem is worsened on trekking/mountain bikes which have balloon tyres as mine does.