I want to move my domain from NSI to 000domains, if I transfer does it involve any disruption to the DNS settings, and is there anything I should particularly be aware of ?

i think no distruption to dns setting.. recently i transfer domain from NSI to one of OpenSRS reseller..

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A request has been received to transfer the domain FOODOM.com
to XXXXX.com, an authorized reseller of the registrar Tucows. This request was entered at Wed Aug 15 00:47:06 2001
by Widya Latief. Note that your nameservers will not change as a direct result of this transfer.
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The registrars are pretty good about this. Since they all use the SRS domain registrar system from Verisign, the only thing that should be effected in the master database is your registrar.

Hope this helps :D