MySQL slow queries – why?

Going to my blog, I’m getting a lot of Service Temporarily Unavailable messages (& so are my visitors!) as well as just slow display. My webhost support pointed to a large number of MySQL slow queries but couldn’t help me as to why they were happening. Here are a couple of them:

# Mon Jan  7 06:29:47 2013
# Query_time: 1.200909  Lock_time: 0.000168 Rows_sent: 0  Rows_examined: 1
use ellenfin_pptblog;
SET timestamp=1357565387;
SELECT ID, post_name, post_parent, post_type FROM wp_posts
WHERE post_name IN ('how-to-create-a-poster-in-powerpoint-2007-powerpoint-2010')
AND (post_type = 'page' OR post_type = 'attachment')

# Sun Jan  6 07:06:33 2013
# Query_time: 1.047694  Lock_time: 0.000118 Rows_sent: 7  Rows_examined: 28
use ellenfin_pptblog;
SET timestamp=1357481193;
SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID FROM wp_posts  INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id) WHERE 1=1  AND ( wp_term_relationships.term_taxonomy_id IN (27) ) AND wp_posts.post_type = 'post' AND (wp_posts.post_status = 'publish') GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC LIMIT 0, 10

I’ve deactivated some of my plug-ins, leaving the following:
Aksimet
Bottom of every post
Comment reply notification
Embedit Pro
Facebook Share
Post-Plugin Library
Pretty Link Lite
Raw HTML capability
Social Media Page
TweetMeme Retweet button
Ultimate Google Analytics
W3 Total Cache
Wickett Twitter Widget
WP Touch

How do i go about figuring out what the problem is?

I’m using WordPress 3.5. The blog is at http://www.ellenfinkelstein.com/pptblog/. Thanks!