I upgraded my 8800 from 4.2.1.101 to 4.2.1.115 (I skipped 4.2.1.108) last night. Everything went fairly smoothly (no hair raising or nail biting) with the following minor exceptions:
- lost all my profile settings (oddly enough I don't recall that happening with previous upgrades, but maybe I hadn't customized it as much before).
- all 3rd party apps migrated over but [as usual] I lost all registration keys and settings, and had to re-enter them. Not a surprise once you know and expect this. Custom themes did not break.
- had to reset TCP APN (as usual since I have a Cingular phone, it loses the Rogers TCP APN info). No surprises.
- temporarily lost SMS detection in BOTH Blackberry Alerts and Pocket Day Pro. This one had me a bit worried, but after a few soft boots and battery pulls, both started working again.
- changing settings in WGarage Reverselookup and AutoLock (both of which reside in Options, rather than being icons on the BB desktop) caused Options (and the phone) to lock up. This happened on my last upgrades too; powering off using the power off button recovers from that but it takes a few battery pulls to fix it permanently. Not so bad if you expect it or are used to it from previous OS upgrades.
Finally, after being satisfied that the phone was working overall, I then went and deleted the demo video, extra languages, PTT, extra themes, etc. and have about 32 MB file free after a bootup. Do I notice a huge difference? Not really (yet).
As a side note, I always had a problem where my calendar invites would get sent out using my wrong address (I have about five addresses set up on BIS). Last time I upgraded, I also had this issue where it used the wrong address and I couldn't set a default. I could set my mail default fine but not calendar. This upgrade was no different, but it used yet a different default address than it did last time (neither of which were the address I wanted to use). I finally got bold enough to delete my CICAL service books (I left the CMIME ones intact) EXCEPT for the default address I want to use, and it worked! Not sure what will happen if I re-send the service books but now that I know for sure what to do, it won't be a problem in the future.
Final summary: I didn't really have issues before so I suppose it wasn't a necessary upgrade. However, there are no negatives either (like slowdowns or memory leaks [yet]). And it was good practice for 4.5.