What particular MySQL queries were slow? Were they custom queries or stock xF queries?
I think a lot of hosts focus on the MyISAM tables performance, but don't pay a lot of attention to the InnoDB tables xF uses almost religiously. At least that's what I've noticed in my own installation.
k. I changed the name of my database name and user.
Part 1
root@host [~]# mysqladmin proc stat
+-------+----------------+-----------+---------------+----------------+------+----------------------------------+------------------------------------------------------------------------------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+-------+----------------+-----------+---------------+----------------+------+----------------------------------+------------------------------------------------------------------------------------------------------+
| 3491 | eximstats | localhost | eximstats | Sleep | 86 | | |
| 13507 | ethos_site | localhost | ethos_forum | Execute | 6462 | removing tmp table | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 13850 | ethos_site | localhost | ethos_forum | Execute | 5937 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 13887 | ethos_site | localhost | ethos_forum | Execute | 5928 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 13971 | ethos_site | localhost | ethos_forum | Execute | 5807 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14066 | ethos_site | localhost | ethos_forum | Execute | 5649 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14114 | ethos_site | localhost | ethos_forum | Execute | 5574 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14144 | ethos_site | localhost | ethos_forum | Execute | 5559 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14174 | ethos_site | localhost | ethos_forum | Execute | 5455 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14180 | ethos_site | localhost | ethos_forum | Execute | 5457 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14198 | ethos_site | localhost | ethos_forum | Execute | 5455 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14255 | ethos_site | localhost | ethos_forum | Execute | 5309 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14271 | ethos_site | localhost | ethos_forum | Execute | 5320 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14301 | ethos_site | localhost | ethos_forum | Execute | 5320 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |
| 14389 | ethos_site | localhost | ethos_forum | Execute | 5133 | Sorting result | SELECT post.*, thread.*, user.*
FROM xf_post AS post
LEFT JOIN xf_thread AS |