I had the same feeling, and posted about it - there are quite a few replies there:
http://forums.omnigroup.com/showthread.php?t=5874
Personally, my advice is to stay away from contexts such as Computer: email, Computer: upgrades, ect.
It just didn't work for me (although for others I guess it does).
Also, I started with a long list of rather specific contexts and crashed and burned on that one as well. So, I reverted to starting with as few as possible and then adding as they became necessary as an improvement. (i.e. rather than trying to think of every possible context (or organizing context) ahead of time, start with as small a list as possible, and grow as necessary as you learn how your GTD/OmniFocus workflow flows). That approach worked for me.
Here is my current list:
@Office
-----Strict (MUST be done at the physical work office)
-----After Hours (for server maintenance when nobody is logged in)
@Calls
@Emails
@Agenda
-----CoWorker1
-----CoWorker2
@Waiting
-----CoWorker1
-----CoWorker2
Errands
Home
Reading
Training