When I first moved my charity's hosting to TSO about 3 years ago they were excellent - fast, stable platform and near instantaneous response to support tickets. So good were they that I then moved by employer's hosting to them, adding a reseller account and persuading 10 or so clients to use them. Now, though, for at least the past year they have become awful - their "cloud" hosting (which is nothing of the sort) is slow and unreliable, with sites frequently unable to load due to timeouts or 503 errors. Their support, likewise, has become very slow, sometimes taking a day to reply. It's a shame, as they were very good and now I'd advise to avoid like the plague! Oh, and their email system has little to no anti-spam filtering, and what there is you can't modify (ie, no white- or black-lists).
UPDATE: I've just found out that they were bought by GoDaddy, and that explains everything! Same thing happened to my previous hosts MediaTemple.