So Microsoft just launched http://www.ieaddons.com/, a web site à la addons.mozilla.org based on Cnet's download.com. There are 526 add-ons at this time:

add-on category number
online protection 22
parental control 3
popup blockers 74 (!)
privacy 109
forms 1
bookmarks 19
business 6
developer tools 47
download managers 65
tools 10
feeds managers 15
offline browsers 23
other browsers 126
animation 2
design 1
digital photo 1
music 1
video 1

It has to be noticed that all these extensions are NOT specific to IE7. They were all (or almost all) made for IE6, meaning that according to Microsoft we have 526 registered add-ons for IE in 5 years of existence of the product. Precisely at the same moment, addons.mozilla.org has 1634 extensions for Firefox, increasing daily.

Even if I don't like the quite poor design of the web site, I have to admit that using CNet's download.com is interesting from at least one point of view : all submitted add-ons are permanently checked with antiviral and antispyware tools... If addons.m.o does not have that, it should probably be added.

But I'll leave the last word of this post to someone called Xepol who posted a comment on the IEBlog:

I can't even begin to describe how hard it is to write IE addons. Firefox clearly doesn't have this problem as everyone and their dog have written plugins.
I've said before that IE needs clear, simple dotNet based surfaces we can code against. FireFox also has Javascript plugins, and that's got to be a must also.
IE's plugins have languished because they are so hard to code for. Just look at the files presented. Download managers, which run OUTSIDE of IE, activeX components that have run inside of IE since forever.
MS makes it too damn hard for just anyone to write a plugin. Just getting a toolbar can be a major episode, seriously language bound to C++ requiring you support numerous, poorly documented interfaces.
We need better,simpler APIs to code against. It is great that there is so much power available, but the simpliest example of a button labeled hello world requires that we know and exploit ALL of that power. The curve is much MUCH too steep.
I would love to code a replacement for the quicklinks toolbar, because it doesn't work the way I want, but I'm a delphi programmer. There are NO succesful delphi examples (the one attempt at a generic framework for delphi results in total hell!)
No no, no, a THOUSAND TIMES no, this should NOT be the problem it is. Simplify, simplify, simplify.
And PLEASE improve the system so that when developing you don't have to reboot or crash your whole damn shell over and over and over just to test and recompile. Plugins should be flushed the pico-second they are turned off.
I can't imagine how you got to this point? Imagine having to continually restart word or visual studio every time you tweaked a script! MS has the skills, it needs to be applied.
Let us write dotNet assemblies, let us write javascript/vb script plugins, reduce the language barriers, and DOCUMENT the interfaces properly.
Not everything requires the complexity of a rocket launch.
Look at the plugins for Firefox, see what real plugins can do.
PLEASE!!!!
Until then, the ie add on site will just be a repository of antique software without any real new innovation (I would be suprise if you get ANY submissions for plugins written recently)