The Mic input on most laptops works fine, but the quality will depend on the hardware and/or drivers on your system. For live recordings though, it should not be a problem.

Tip: Use an uni-directional microphone (e.g. an electret condenser, with a 'telephoto / zoom' setting which cuts out extraneous noise from around you (i.e. either side of the mic)). There's nothing worse than your live recordings being ruined by the clink of glasses and the off-key bellowing of the guy on the next table during the choruses* ... Also, consider recording in Mono, for the same reason.

If recording in a club, make sure that the mic is physically isolated from the table - (a bean bag works), as any knocks near it will be really loud!

AP

* usually me.