I just counted and I'm signed up with 142 companies. I have them all bookmarked and saved in folders, Sassie, Prophet, Shopmetrics, etc, and one big catch-all for the ones with proprietary portals.
If I'm planning a route, I will actually open and review every one of those tabs, looking to see if they have jobs in my target town or on the way. So about three times a month I see every one of them. I can do an "open all in tabs," platform by platform, which enables quick log in since all the log ins are on the same part of the page. It takes me about an hour to see them all, closing the tabs that don't have jobs, leaving open the ones I might want to work into a route.
When I'm not looking for a route, I just look at any email that catches my eye with a bonused shop. So if you rely on emails to do shops, you'll miss a lot, because a lot of them never send emails. (I get an average of less than 100 a day, and about 20 of those will be from three particularly annoying companies. So clearly not all of them send emails very often.)
It would be a good practice to check all your companies about the 20th of the month (when bonuses might be creeping up) and about the 3rd of the month (to catch the companies who load their jobs at the beginning of the month.
Time to build a bigger bridge.