Can't beat playing to a drum machine with a good tight backing track. The problem with a metronome for me is nothing is happening between the clicks, so you can end up with uneven loose rhythms as you rush to meet the click. A backing track with hihats, kick and snare is much easier, throw in some rythmic chopping and you're away. An excellent but very difficult way of nailing solos that require exact timing (eg neoclassical pieces) is to score them out in midi first then play along. The beauty of midi is you can change the bpm to match your skill level then gradually increase it as you get the licks down. If you listen to Rusty Cooley, Theodore Ziras and Yngwie Malmsteen you will notice they play along to a keyboard - with the exception of Yngwie the others are actually playing to a machine. This increases accuracy by a factor of 10 and increasing your abiltiy to get good fast BUT it is very difficult. Also, unless you are consistantly playing straight neo-classical stuff it can sound a little sterile when things get overly accurate an dyou lose the 'swing' feel.