It took me less than 5 minutes of using Mailplane to make my purchase over a month ago.
I still use Entourage to handle 2 of my GMail accounts since I want that information stored locally in my hard drive. Others may use different email programs such as Apple's Mail. My previous choices for an email program have been Mailsmith and PowerMail, but I've used Entourage for many years now. Apple's Mail has finally gotten better, so that may be the current choice of many Mac users.
It should be obvious that if all a person needs is to receive GMail's email, Mailplane may not be worth it. For people with a single GMail account, Mailplane may not be worth it.
On the other hand, here are some of the advantages I've found for my use:
-Speed. When checking mail and switching among multiple addresses, and while working with email on a daily basis. Also, I like to report the spam I receive. Using a filter does NOTHING to fight spam. It merely helps my Inbox stay clean. Using Mailplane I can quickly check 4 accounts, and report the spam I receive. As I mentioned I use Entourage, and I set it up so that it NEVER receives any of my GMail spam.
-Labels. I have a variety of Folders set up in Entourage for my GMail accounts. This works fine, but Mailplane's approach is also efficient and faster. My rules don't always work automatically in Entourage, but so far they always work in Mailplane.
-Search. Mailplane's searches are superior to those of Entourage -although Entourage is great in this regard and very flexible-, and I guess this also applies to Apple's Mail. I can find anything on Entourage, but with Mailplane for example I can view a whole thread in a single window. In Entourage I would have to select and view each email individually. Speed and a more efficient workflow again play a role.
-Screenshots, attachments, integration with other applications, chat, etc. I don't use these features that much, but for some users these are important.
Mailplane is not something that everyone will want or need. For some it will be expensive. I actually bought it when it had a nice discount. Still, for many users it is definitely worth the $25 or $40 for up to five family members living in the same household.
After using it for over a month I would hate to be without it.