SiteGround in years past (pre-2007) did not disclose much about its people and their location(s). More recently they've become somewhat more transparent, professional, and personable. They have been and are even more so today a decent source of inexpensive shared hosting with frequent promotions and discounts. Since 2007-2008 occasional slow service and outages seem to have become a thing of the past on individual Siteground shared hosting accounts I use or maintain. Response times under 1s, zero to minimal downtime. These accounts reside on dedicated servers leased from ThePlanet (Houston, TX), which is also used by Site5, WebFaction, and many other hosts. Siteground's VPS and DS accounts are on servers based in Chicago and Virginia. (This may have changed; they now specify Houston, Dallas, and Chicago in 2010 and it's not clear who is providing the servers.) The 2010 VPS plans seem overpriced.

On the downside, Siteground has always been exceptionally aggressive about trying to lock in control of your domains, which they make very hard to transfer out. They have been quietly increasing their fees and have become more of a "you better read the fine print" type of company. As of 2009-2010 there is a bad "bait and switch" odor to the way they play with fees and ramp up prices over time. SiteGround is the only host I've encountered where they increase your costs over time for the same service and don't even try to explain why. They are still overselling bandwidth and storage in their shared server packages, but they are much more careful with their reseller accounts.

SiteGround's account administration and support interface is remarkably simple and effective after several improvements to it since 2006. Their customer service and tech support people are in Sofia, Bulgaria. Seemingly comprised of several guys (or one very active guy) named Alexi (that's a joke), SG tech support is surprisingly capable and fast. (Guaranteed 15 minute response time for every support contact, and it's usually faster than that.) Support and performance seems to have improved over the years, which is the right way to go. Several years back, I had some frustrating incidents with them, but I was always able to fight through to a resolution, and they had a pretty good tolerance for this. (Sometimes you just have to be aggressive and make it clear you know what you're talking about. Support people for shared hosting have to deal with a lot of morons.)

Generally I think low end packages from big resellers (and big resellers in general) should be avoided, and I've been through some rocky moments with SG, so it says a lot that I see them as a decent choice. Surprisingly, I have never had problems with email on Siteground's shared hosting accounts being blacklisted because someone else on the same server was spamming folks. This seems to be a fairly common occurrence; I've had it happen with Nexcess and Media Temple accounts.

SiteGround uses cPanel, and they're good to go with Drupal, Joomla, Wordpress, and other open source applications they actively support. (PHP runs as a CGI process.) They have a standing offer to migrate your existing site and mail system to their servers at a discount. They will then credit you with whatever time remains of your already paid up, current host. The main downside with SiteGround is their attempt to become registrar for all your domains and extract fees for "add-on domain slots" and other services you probably don't need. However, the add-on slots and the tightly restricted number of domains you can put on a reseller account are a way for SiteGround to mitigate the worst effects of overselling capacity. 

Because of their presentation and semi-offshore status, I've never really trusted SG as much as I probably should. They maintain good uptime and response time figures for even their lowest-priced shared accounts, which are probably still their bread and butter. For many small to mid-sized operations, SG is more than adequate hosting. They're not very personable, however, although they previously seemed to be taking steps to move in the direction of personalizing their brand and speaking more directly with customers. That has a lot to do with how I regard a company, so it hurts my impression of SG.