I'm a SQL Server DBA who has been using both tools for a while now and I cannot understand how anyone would choose Management Studio over Enterprise Manager. Here are a few of my beefs:
1.) MS takes much longer to load, even when you configure it not to connect on startup.
2.) I totally agree with another post I saw on here. For nearly any task, it takes significantly more clicks to get it done, and there are longer delays in between clicks.
3.) EM allowed external tools to be configured and EM would pass parameters for the current server and database. MS does not have these parameters available for external tools. It does provide a bunch of useless parameters such as the current project directory. This is of no value to me.
4.) The new online help is harder to use. Searches return more irrelevant info than I've ever seen. It also takes a long time to load and all the increased search capabilities clutter the screen. SQL 2000 Books Online was faster and easier to use. I don't use 2005 Help at all since Google is superior.
5.) Error messages often give misleading information and some don't even use correct English.
6.) When starting a job, the menu says "Start Job At Step", leading you to believe you can select a step. It always starts at step 1 regardless.
7.) When displaying database file properties, it doesn't show space used as the Taskpad did in 2000. Yeah, you can use the new reports but that takes longer to get to.
8.) I have no faith in the new reports anyway. I deliberately created a blocking situation to see what the blocking report would display and after refreshing several times, it never even detected blocking.
9.) When drilling down on an object, you get far too many windows. I don't like all the extra clutter on my desktop.
10.) No easy way to show database role permissions as there was in EM.
I only use SSMS on our SQL 2005 servers because I have to. I far prefer the older tools and still use them on our SQL 2000 servers.