I am using 5800 since last 8 months and updated firmware (no custom fw) periodically. I never felt 5800 performing slow. I would rather say its a multimedia workhorse (for that price). It can do any job thrown at it by todays standards.
People say that its touch sensitivity is bad but before using it you must know that it has resistive touch and it needs to be pressed a little to register touch. Better way is to have it operated by your thumb nail. I personally like resistive touch as there will be no accidental touch which is annoying in capacitive touch.
Camera is fine, not good under dark area. But in daylight it takes amazing detailed pictures. Compared to Spica it has dual LED flash.
Music output is very good, very rich i would say. It may not sound extremely loud in earphones. But sound output is enough to rock any audiophile’s head. Also, stereo speakers are awesome, i must say.
Comes with OVI Music voucher (i think unlimited download). Best way to get licensed songs with quality.
Comes with lifetime free navigation worldwide. Also the battery backup is good.
OVI app store is decent enough to have freebees everyday.
Comes with 8 GB on board (microSD). Also it has high resolution display 360x640 as compared to Spica’s 320x480.
No matter what people say about S60 v5 but it is the best geeky OS ever. You will find a new app everyday (almost). Costomised firmwares and modding makes this os unbeatable.
Apart from making phones Nokia is more interested in providing class leading software support. It keeps updating things every now and then. I personally like that. Your phone never go old if you keep updating.
No offence to Spica fans (me too like it btw
) but i think 5800 is difficult beat at this price band. Only minus is that 5800 doesn’t support DivX codec. But there are lot of converters available to convert to mp4.
I did not compared 5800 with Spica point to point so did not mentioned much about Spica (i know large amount of Spica fans out there).
Thanks for reading such a large post, i was sitting free so thought why not write something. 
PS: You need to hack it to utilise its full potential, free
.