0. If nothing works for you... :
No downloads, no seeding , active torrents are in red, no green net-status, in trackers' tab - none are connecting... check this:
[1] If you have a router - check that your port is still being forwarded and is opened [Control-G->setup guide] and for both TCP + UDP
[2] Check that you have enabled/excluded the new release in your Windows firewall/3rd party firewall (replacing the old rules)
A. For fixing CPU-load/memory-issues/stability:
[1] In pref.->advanced->Disk Cache Make sure :
1a. ->Disable Windows caching of disk writes/reads - are both checked
1b. ->reduce memory usage when the cache is not needed - is unchecked
[2] Make sure pref.->advanced->gui.transparent_graph_legend is false
[3] Win7 users might experience uTorrent process not closing properly.
It is suspected to be caused by a Microsoft IPV6 issue. Those command lines can assist by disabling IPV6 in your system:
netsh int 6to4 set state disabled
netsh int teredo set state disabled
[4] On Win7 - you can also set the new advanced setting: net.disable_ipv6 = true that supposes to prevent it.
B. For improving low speed issues:
[1] Make sure your upload speed limit is correctly set as follows:
1a. If you have "Banwidth->Apply rate limit to transport overhead" enabled (recommended) -
set the upload limit to about 80-95% of your connection's maximum upload-speed/cap.
This is required so to accommodate for 1) + 2) above, limiting the total of
upload-payload + download-acks-overhead
You can test your connection speed @ http://speedtest.net or use the options->setup-guide (control-G)
1b. If you have "Bandwidth->Apply rate limit to transport overhead" - disabled -
set the upload limit to 70-80% of your connection's maximum upload-speed/cap.
This is recommended in this case, but not required, though.
You can set it to as low as the actual seeding-payload speed you like to have.
In both cases you can use a different upload speed limit setting at pref->bandwidth->"Alternate upload rate when not downloading"
Test your download speed again now with this (test torrent...) This step should be enough for most users that upgrade!
[2] Settings that might improve (reduce) your overhead:
2a. Set pref->advanced->net.uTP_dynamic_packet_size =false
2b. Set pref->advanced->net.utp_initial_packet_size = 8 (use MTU size)
[3] Set pref.->advanced->bt.tcp_rate_control = false
[4] If you want to try and reduce your ISP's throttling:
Some ISPs are more "sensitive" to UPD (uTP) traffic. You can reduce the use of uTP by -
4a. Support only uTP incoming connections by setting pref->advanced->bt.transp_disposition = 29
4b. Alternatively - disable the use of uTP by pref->BitTorrent->Enable Bandwidth Management = unchecked
[5] To improve availability of peers, you might want to clean up the bans uTorrent imposes on PEX peers due to 'message flood'. So, for torrents running/active for a long time, it might be helpful to perform every couple of days:
right-click->advanced->reset bans
right-click->advanced->clear peer list
Finally, For users who like to experiment with uTP - try to reset it to UNLIMITED speed disabling the new: Bandwidth->Apply rate limit to uTP connections .
The theory is that this will give you high speeds, w/o effecting other Internet traffic.Good luck with it ! and report back here ...
C. For improving Internet choking / router issues:
[1] First, make sure you have set a proper upload speed limit (B.1 above) and that your max # of connections/slots are per the setup-guide
[2] Change setting per B.2a&b above
[3] Set your pref->advanced->bt.connect_speed = 5
[4] Set your pref->advanced->net.max_halfopen = 8
[5] Disable the DHT network
[6] In pref->connection - Disable NAT-PMP port mapping.
Make sure 'uPnP port mapping' is unchecked if you've manually forwarded you port in the router.
[7]
D. If you feel your multimedia player throttles your speed (Win7/Vista):
If you've noticed this strange behaviour (mostly with high speed connections) when running a player/recorder/streamer app -blame Microsoft... and modify/create this registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Multimedia\SystemProfile\
Name : NetworkThrottlingIndex
Setting to - FFFFFFFF will make it not throttle .
Other values may adjust the amount per the above article.
E. For minimizing possible "privacy invasion" issues:
1. Settings:
Pref->general->send details when checking for updates - unchecked
Pref->advanced->gui.report_problems - false (do not send crash reports)
Pref->advanced->gui.bypass_search_redirect - false (bypass BT inc search server when searching)
2. To avoid installing of the TOOL-BAR make sure you follow this:
You may also look here for some more advanced methods on how to uninstall it ... 
F. Bypassing known bugs:
1. Bug: After running for 22 days - uTorrent will not handle properly uTP connections (bad timer issue, relevant only for builds 21586 and below)
Bypass: Upgrade to the latest build, or close & open uTorrent at least once every 22 days ...
2. For Win 7/x64 users - not being able to kiil uT process - see A[3-4] above ...
3. Resetting Transfer Cap history - will not quit the "stopped" state , caused by the cap limitter. A bypass solution is here.
4. TBD ...
G. When the speed is going over your set limits:
See that your Perf.->bandwidth->Apply rate limit to uTP connections is checked...
H. For problems downloading the "help file" :
- Get the latest copy from here
- Extract to your settings *.dat files location
- Rename to utorrent-
For example - for release 2.0.1 build 19248 - utorrent-201-19248.chm
for release 2.0.2 build 19648 - utorrent-202-19648.chm
for release 2.2.0 build 23071 -utorrent-220-23071.chm
Other troubleshooting related links/threads:
- Speed related issues: http://forum.utorrent.com/viewtopic.php?id=15992
Thanks for such a great post and the review .