I have all mail since 2001 (around 80'000 messages) in my google (apps, paid) account. While the web interface is still acceptably fast (as long as I don't browse my All Mail label), but the iphone (and ipad) frontend has become unbearably slow in the last few weeks.
It opens quickly, loads the locally cached page and then it's just spinning and spinning for up to 5 minutes before it either reloads the page completely, signs me out again or finally displays the new mail.
Considering this is a product from a company that places so much importance on speed, this is completely inacceptable, IMHO.
I had the same problem with the iPhone web UI. Delete the local HTML5 database from Mobile Safari, then kill and restart Mobile Safari, or restart your phone. Once I did this, iPhone web gmail was fast again.
I started having this problem with the mobile Gmail interface a few weeks ago too. The solution was to stop using a bookmarked inbox URL. When I use the http://mail.google.com/a/mydomain.com/ URL instead (and go through several redirects to the mobile site), my inbox loads nearly instantly every time.
I have no idea why this is the case, but it solved my problem.
My android gmail app is just as fast as the web. I have 35k messages, about 1.5gb. The web interface is slowish, but I haven't noticed the phone app being any slower.
It opens quickly, loads the locally cached page and then it's just spinning and spinning for up to 5 minutes before it either reloads the page completely, signs me out again or finally displays the new mail.
Considering this is a product from a company that places so much importance on speed, this is completely inacceptable, IMHO.