Visual Studio loading symbols
Solution 1:
Debug -> Delete All Breakpoints ( http://darrinbishop.com/blog/2010/06/sharepoint-2010-hangs-after-visual-studio-2010-f5-debugging ) After that you can use them again, but do it once. It will remove some kind of "invalid" breakpoints too and then loading symbols will be fast again. I was chasing this issue for days :(.
Solution 2:
Another reason for slow loading is if you have disabled "Enable Just My Code" in Debugging options. To enable this go to:
Tools -> Options -> Debugging -> General -> Enable Just My Code (Managed Only)
Make sure this is checked.
Solution 3:
Configure in Tools, Options, Debugging, Symbols.
You can watch the output window (view, output) to see what it's doing usually. If it's really slow that probably means it's hitting a symbol server, probably Microsoft's, to download missing symbols. This takes three HTTP hits for each file it can't find on every startup - you can sometimes see this in the status bar at the bottom or in e.g. Fiddler. You can see which modules have loaded symbols in Debug, Windows, Modules whilst you're debugging.
Symbols mean you get useful stack trace information into third party and system assemblies. You definitely need them for your own code, but I think those get loaded regardless. Your best bet is to turn off any non-local symbol sources in that menu and, if you're loading lots of symbols for system assemblies that you don't need to debug into you can temporarily disable loading those to speed up debug start - but they're often useful to have loaded.
Solution 4:
Just had this problem.
I fixed it by navigating to:
Tools -> Options -> Debugging -> Symbols
Then unchecking all non-local sources for Symbol file (.pdb) locations
e.g. Microsoft Symbol Servers and msdl.microsoft.com/download/symbols