I have been using BSNL 256kps from Jan 2005 but recently switched to using Tata Indicom as my primary connection for the last 5 months.
Speed 128kbps, unlimited data download plan. It has generally been reliable and good. I have a wireless modem and use it for my laptop and desktop simultaneously, as I am following the commodities and NSE together. I find the speed adequate for intraday data feed.
The customer service is horrible, very pathetic. So if you face downtime its trouble. For this I have BSNL 256kbps Broadband as a backup connection, data download is 1GB per month.
Generally BSNL connection provides very good speeds and is excellent value for money. The problem I face with BSNL is specific to my building due to extended cable length.
Often in our area BSNL service is erratic, hence have Tata as my primary service connection.