I have had a few issues since I installed the Android 2.1 update, on my Sprint HTC Hero, but was able to fix quite a few of them myself. Below is a list and my personal commentary on each.
-Web Browser: The Google homepage kept displaying in either French or Spanish. I do not know exactly how I fixed this issue, but it seems to be gone now. I think it was a combination of clearing the web browser's cache and messing with settings on Google's homepage.
-Google Navigation: The blue arrow icon just would not show up in my app drawer after I installed the update for Google Maps. I tried uninstalling it and reinstalling it a few times to no avail. I finally decided to try rebooting the handset and that fixed it.
-Loss of Mobile Data: This problem still arises once in a while, however, either a simple reboot or toggling the Mobile Data widget on and off seems to rectify this. I do not experience this problem often enough to be concerning. One thing I do notice is that sometimes my handset likes to switch 1xRTT mode for an indeterminate amount of time after a phone call or while downloading an MMS image. Oh, and one more thing I noticed is that when I attach an image to an SMS, it compresses the picture WAY more than it did in Android 1.5. I used to be able to see several hundred kilobyte images in Android 1.5, but now they are reduced to under 10 kilobytes at maximum and the overall image resolution is very tiny.
-Ring Lag: My handset tends to waver from starting to play my ringtone between two and four rings on the caller's end, which is faster to slower than Android 1.5, respectively. I also noticed that after attempting to call my handset twice in a row, it would kick me right to voicemail and my data connection would be at 1xRTT. This does not happen consistently though.
-Repeating and/or Late E-Mail Notifications: This one I am still in the process of trying to figure out what is wrong. The scenario is that I will receive an email and get a notification, but if I do not check it for a while, I will get another notification for the same email some hours later. Now, it could be that the email's notification is just being delayed. I noticed one time that I had a new email, but the notification sound did not occur until some time later. If anyone has any ideas about this one I would be very interested to hear them.
-SMS and Keyboard Lag: I have noticed that upon opening the SMS app the first time, there is quite a bit more lag in loading previous texts than there was in Android 1.5. I actually used to have text message threads with over 600 texts in each and they would load quickly in Android 1.5. Additionally, the virtual keyboard seems to lag slightly more than it did in Android 1.5.
As you can see, most of the issues I have experienced were remedied after I did a little research. However, the email notification problem and general lag with the virtual keyboard still remains an issue, as does the inconsistent mobile data phenomenon.