A disclaimer: we use Redhat quite a lot at work so its entirely possible I would be complaining about distro X if we used that.
Firstly, we've used Redhat for a long time. The first time they really annoyed me was when they ditched their desktop offering to purely concentrate on their "enterprise" version, leaving many users especially us early business users in the lurch. But business is business I suppose. More recently I become annoyed at them because of their poor system management tools and lousy support.
An example, last year I set up a machine with Redhat and xen. Now this was on their point one release of Redhat 5, they started trumpeting their virtualisation offering with the point zero release so you'd think it would have been pretty smooth: it was painful. As it turned out they did not support a 32 bit version of their own OS running in a 64 bit version. The more I talked to their support the more I realised I knew more about their operating system than they did.
Their update and management infrastructure is dreadfully sluggish and clumsy. Operations that should error sometimes just silently fail. But the main issue I have with Redhat is the lack of community. They've hived off what in my opinion is the best thing about open source, i.e. the community, into their Fedora distro. Now obviously Redhat's enterprise offering is based on Fedora but it isn't Fedora - some things are different. Often when I've googled a problem I've found nothing from Redhat users, some from fedora users but more likely answers from CentOS users. This is a sad reflection on Redhat.
To summarize, would I now recommend Redhat to a someone. Well it depends on who you are. A home users: definitely not. A small business users: probably not. I large enterprise user: grudgingly.
David Holden